Leniency system of confession and punishment refers to the system in which the accused voluntarily confesses his crimes, admits the accused criminal facts, is willing to accept punishment, and can be dealt with leniently according to law. Under the inducement of leniency, the accused should not only measure the cost and loss of "admission of guilt" or "non-admission of guilt", but also consider the profit and gain of "admission of punishment or non-admission of punishment". The implementation of leniency system of confession and punishment involves multiple choices of "Plead guilty" of the accused, and also involves the cooperative interest game between the accused and judicial authority. Therefore, from the perspective of cost-benefit theory, we can better understand the connotation and internal relationship of "confession", "admission of punishment" and "Leniency" in leniency the system of confession and punishment.