A novel adaptive peak inductor current limit for double hysteresis Buck working in DCM is proposed in this paper to improve efficiency at light load. Due to constant peak inductor current, conduction loss of double hysteresis Buck is the main reason that impose restrictions on efficiency at light load. To overcome the problem, peak inductor current will decrease adaptively while the load changes from heavy to light by sampling time of sleep period. Furthermore, a dynamic quiescent current control method is adopted to reduce quiescent loss of double hysteresis Buck. The propose Buck chip is fabricated in 0.18μm BCD process. The experiment results show that the maximum-improvement of efficiency is 3%