Our study explores whether longer audit tenure can promote the market efficiency to reduce information asymmetry. Under an inefficient market, information cannot response effectively to the market, which causes a problem of information asymmetry. Therefore, it requires the government to protect investors through the enforcement of mandatory auditor rotation policy. On the other hand, under an efficient market, information has been fully reacted in the market, so interventions from government are unnecessary. There are two findings in our research. First, we find that the longer the audit tenure is, the more the efficiency of the market can be improved. Second, with the comprehensive effect of the two kinds of audit tenure, audit firm tenure can significantly improve the efficiency of the market, while the effect that audit-partner tenure can improve the efficiency of the market is insignificant.