This paper explores the reasons for the disappearance of the relationship between corporate governance and stock performance, and puts forward the investor trust hypothesis and the pricing efficiency hypothesis to examine idiosyncratic risk and pricing efficiency is an intermediary variable between corporate governance and stock performance. The results show if company have better corporate governance, then will have high idiosyncratic risk in then future, to support the investor trust hypothesis; and the better corporate governance company will have high pricing efficiency that also show to support the pricing efficiency hypothesis. It is further found that idiosyncratic risk is an intermediary variable between corporate governance and stock performance, that is, the better corporate governance company will not only have good performance in the future, but also idiosyncratic risk will more strong. The results show that idiosyncratic risk is the main reason for the disappearance of the relationship between corporate governance and stock performance.