Timing financing theory holds that when listed companies are overvalued, they will increase equity financing. Different from previous studies, this study explores the mechanism of timing financing theory in China from the perspective of financing efficiency. Through the empirical study of M & A cases of Listed Companies in China from 2007 to 2018, it is found that the timing financing behavior that increasing equity financing when overvalued reduces the positive impact of equity financing on M & A performance. Further research found that the mediating effect of the financing efficiency exists, that is, the timing financing behavior does no increase listed companies’ financing efficiency, so it can not help listed companies create value through M & A.