The cartels may injure the fairness of market competition and most of the authorities around the world have implemented Antitrust Law to eliminate them. The leniency policy is a regulation which can eliminate the cartels. The purpose of this article is to investigate the effect of this policy. We extend the model of Silbye (2012) and establish a two-stage game theoretical model. The first stage is before the beginning of antitrust authority's detection, and the second stage is after the beginning of antitrust authority's detection. First, we apply the leniency policy in Taiwan, Japan, the U.S.A. and the E.U. into the basic model. And then we get the subgame perfect equilibrium of firms in each stage. We find the leniency policy in the U.S.A. has the most effective impact on promoting the incentive of the firms to report early.