With the development of automobile lightweight technology,the use of aluminum alloy and other lightweight plates is gradually increased in automobile design,which puts forward new challenges and requirements for coating process design,process management and quality control,especially for coating pretreatment process design,material selection,process parameter control and quality management.This paper mainly introduces two kinds of pretreatment technology of steel aluminum collinear coating production line.From the process point of view,it mainly introduces the key process requirements and management points such as degreasing,surface blending and phosphating,and compares the pretreatment process of phosphorus free conversion film,and at the same time,the corresponding electrophoresis of phosphating and phosphorus free conversion film pretreatment methods for galvanized steel sheet and aluminum alloy plate is carried out the compatibility of the coating was analyzed and studied.