The form variation is an important feature for taboo in the Tang dynasty. The popularity of folk characters makes the avoidance of characters in monarchs' names appear in common characters. This taboo appears not only in the form of common characters, but also in the folk characters which are related to the common characters. This leads to the appearance of special folk characters taboo in the Tang dynasty. Basically speaking, this is a reasonable result when the development of taboo system and the form of folk character gets fastigium. Due to the change of focal point in taboo and the popularity of block printing, the taboo of folk characters can not develop without its procreant conditions and gets to its end after the Song dynasty.