An effective governance mechanism has an important impact on the efficiency of investment. On the basis of principal-agent, the agency cost is subdivided into supervision cost, guarantee cost and residual loss. After sorting out, the relationship between accounting conservatism and non-investment efficiency is summarized and analyzed from these three aspects. It is found that the relationship between accounting conservatism and over-investment is relatively clear. That is, robustness can alleviate the conflicts between shareholders and managers and shareholders and creditors by acting on three different agency costs, so as to restrain excessive investment and reduce inefficient investment. As for the relationship between accounting conservatism and under investment, existing studies have not reached a unanimous conclusion.