The paper makes an in-depth analysis on conventional bridge rectifier, the working process of boost chopper, control method, input changes in current law and etc. Based on it and according to the principle of energy equivalent, the relationship between chopper conduction ratio and step-up ratio is given, and makes explanation of boost range. By grafting circuit connection and introducing non-linear devices, an improved boost-buck chopper is proposed. Through the method of capacity divider and inductive energy storage, the dual control of boost and buck can be easily achieved which has the advantages of a wide range of voltage regulation, less input harmonic current, convenient control and achievement and etc. so it can be applied easily to a variety of low-power voltage conversion device.