Judicial transparency index improves the openness and transparency of judicial system via quantitative assessment， and has become an important measure in China nowadays. The legitimacy of judicial transparency index includes: first， procedural openness， procedural rationality and practical rationality， According to the practice in the countries over the world， procedural openness has three aspects， open trial， open evidence and open judgment，i.e.， the reason and basis of judgment should be fully explained. Second，rule of justice under mutual functions of the subject and object. The formation of judicial transparency index focuses on the supervision， moderation and the response of justice. This paper contains some empirical studies based upon the Judicial transparency index of Zhejiang courts and Wuxing district court. We may find limitations of judicial transparency index as: the arbitrarinessof setting up of index， the subjective tendency in index weight and assessing subject， the unreliable questionnaires， the imbalance between subjective and objective index， the limitation of methodology． Based on the analysis of the local practice， four measures can be taken to improve the designs. First， managing the relation between high-level design and local practice. Second， building scientific index evaluation system by general method for quantitative assessment of social science. Third， stress on the key point of index evaluation， that is to say， installation of index should focus on the evaluation of the use of new media， the reasoning of written decision， and quantitative assessments should be centered on the trial. Fourth， a balanced use of Judicial transparency index requires the dialectical treatment and reasonable explaining the information revealed by the index in certain circumstance. Building the scientific judicial transparency index is a technical improvement per se，which is a gradual reform process rather than institutional innovation. China is at the start-up phase of rule of law， still lack of some basic conditions supporting the classic rule of law. So， judicial reform may not be expected to be prefect. In this context， gradual technical improvement has more feasibility and realistic possibility． In the long run， there is room for us to move from technical improvement to the institutional innovation.