The emergence of automatic transmission has brought great convenience to people driving vehicle.With the continuous development of science and technology,automatic transmission has almost occupied the entire automotive market.There are also many types of automatic transmission in the market,and their principle and structure have significant differences.This paper gave a detailed introduction to the current mainstream automatic transmissions,helped maintenance engineer have a comprehensive understanding of various types of automatic transmission,master the principle and structure of transmissions,and provide a clear analytical approach for maintenance engineer by introducing automatic transmission maintenance and dissecting classic cases.This paper aims to help maintenance engineer on quickly fault finding,troubleshooting and maintenance service efficiency improving.