Non-literal language, including metaphor, humor, pun, idiom, irony, riddle and so on, is termed figurative language. To understand non-literal language, it is necessary to break the mind-set and ignore the literal meaning to obtain the figurative meaning implied in the expression. Conventionality is one of the most important factors in non-literal language processing. Conventionality is the degree of being conventional, among ″a population that has implicitly agreedto conform to that regularity in a certain situation out of preference for general uniformity″, and it refers to the relevance between a certain expression and one of its metaphorical meaning in non-literal language-processing. Non-literal forms with high conventionality include conventional metaphors, idioms, etc., which are stored in the traditional culture and people's mental lexicon in a particular society, being highly conventionalized in daily life. Forms with low conventionality, such as novel metaphor, humor, riddle and irony, need to be understood in a specific context through association, reasoning or insight, because they are far from conventionalized. There are also some non-literal language constructs between the two poles with medium conventionality, such as puns and xiehouyus, which have both salient conventional meanings and novel non-conventional meanings. Until now no scholars have compared the cognitive processing of varied non-literal language forms according to conventionality, and there is no unified theory to summarize and guide the segmented and isolated research projects of Chinese non-literal language. Using relevant empirical results in recent years, the researchers of this paper take the degree of conventionality as an axis, and discuss the positions of different non-literal language forms on the axis with their own cognitive difficulty and complexity, finding that varied types of Chinese non-literal languages act as a continuum on this axis. The authors attempt to clarify a neuropsychological processing system by constructing the Conventionality-oriented Progressive Hierarchy (CPH) Model. Language constructs with low and high conventionality are placed at both ends of the axis respectively, and those of medium conventionality are somewhere in the middle of the continuum. For less conventional language forms, people have to process the literal meanings first, and then infer and interpret non-literal intentions according to context. For types with high-conventionality, which are usually conventional expressions in daily life, the processing mechanism is close to that of literal language because their highly conventional non-literal meanings can be directly accessed through a strong context. Moreover, as for non-literal language forms with medium conventionality, both the literal and non-literal meanings are activated and processed simultaneously or successively, and either of the two meanings can be accessed and maintained in the late-integration processing. By contrast, non-literal constructs with high and low conventionality suppress their literal meanings first in order to obtain their non-literal meanings. According to the CPH model, the authors have sorted the processing characteristics of various non-literal language forms, and summarized the following basic features of a non-literal language cognitive mechanism: (1) the more conventional the figurative language form, the easier and quicker it is to process; (2) processing non-literal language constructs with lower conventionality needs more involvement of the right hemisphere of the brain, in which case participants often have to relate non-conventional meanings to non-linguistic factors, so the right hemisphere, which has corresponding cognitive functions such as association, imagination and insight, plays a more important role here; (3) Context and familiarity have a mutual restraint effect, that is, for all non-literal language forms, high familiarity with strong context is the easiest to process, while low familiarity with weak context is the most difficult situation in which to access figurative meaning. High familiarity with weak context, as well as low familiarity with strong context, can make up for the deficiencies of one side with the advantages of other, making it comparatively easier to process the corresponding non-literal expressions.