Since the beginning of the matrix converter, the commutation strategy research on it is a lot. Based on the direction of current detection and voltage direction of fourstep commutation strategy have been extensive research and application. Some researchers have analyzed the four steps in flow process and the output waveform, But few of them, to the difficulty 、the reliability of the output waveform and waveform quality for further analysis and comparison. Based on the deep analysis of the commutation strategy and combined twoway switch ，this paper presents a detailed introduction to the four step commutation strategy. On the basis of ensuring the reliability of the flow changing and improving the quality of waveform, the correctness and effectiveness of the conclusion are verified by the MATLAB simulation method, and the advantages and disadvantages of two types of fourstep commutation modes are analyzed and compared.