Abstract: The reform of leniency system has offered the system space and development opportunity for sentencing de-
fense. From the status quo of legislation, there exists the absence of system of sentencing defense under the leniency system. It lies in the two specified institutional dilemmas. The first one is the lack of legislation on the level of standardization which is shown in the two dimensions of sentencing procedure and lawyers on duty. The second one is that there are too many problems on the practical level which are shown in the system of the lawyers’ participation and defense specialization. To tackle such di- lemma, the sentencing defense under the leniency system should be perfected from the three aspects: construction of sentencing procedure, defense lawyers’ participation and specialization of sentencing defense. On this basis, the sentencing defense can be conducted effectively under the leniency system.