In this study, we use a game-theoretical model to investigate the effect of the system of whistleblower protection on the employees and the companies. Whistleblowing can be treated as an implicit supervisings mechanism to prevent senior managers’ possible illegal activities. However, if the whistleblower are internal employees, they may be subject to companys’ revenge. Therefore, an effective whistleblower protection system should be established to encourage employees to blow the whistle. The results show that under a sound framework for whistleblower protection system, the employees’ willingness to blow the whistle can be improved, but the companies might still take illegal actions if they can receive large benefit from dismissing the whistleblowers.