Abstract: A current mode buck DC-DC converter with using a load adaptive method (LAM) to keep high efficiency within wide load current range are presented in this paper.The converter used error signal and a load adaptive threshold to flexible switch in pulse width modulation (PWM) mode and skip mode according to the load current.In skip mode,the converter can reduce switching loss and quiescent consumption.Through analysis and derivation,the relations between load adaptive threshold,inductance peak current and load current were inferred.Simulation results implemented in 0.5μm BCD process shows that,under the condition of 12 Vinput and 3.3Voutput,When the load is light,the converter enters LAM mode,the efficiency is much higher than the same load in PWM mode,especially in I_Load=10mA,the efficiency of PWM mode is only 45.6%,but in LAM mode the efficiency reach 80.1%.