This article reviews studies on the impact of mandatory mechanisms and voluntary mechanisms on carbon emission reduction and introduces the mechanism design of the Saitama Target-Setting Emissions Trading System (Saitama TSETS). Through the analysis, we find that there is no research on the impact of the second phase and whole phase of the ETS on carbon emission reduction in Saitama Prefecture. Moreover, the Saitama TSETS seems more like a voluntary environmental mechanism. Therefore, in future studies, the author will use a difference-in-differences (DID) method with propensity score matching (PSM) method to evaluate the impact of the second phase and whole phase of the ETS on carbon emission reduction in Saitama Prefecture, and add more factors to control the difference between the control group and the treatment group. The author suggests that these studies may be important references for the continuation of the Saitama TSETS in the future and the development of a nationwide ETS in Japan.