This paper studies how to improve the quality of automobile bodywork. The complexity of bodywork decides variety of it's error. The station and primary factor which cause error is inconstant change and using correlation analysis can find out the primary factor. With an project given, the theory of correlation analysis for dimension variation of bodywork is discussed through correlation analysis and the layer structure of the bodywork,the state in which the error happened can be found out. How to use eigenvalue and eigenvector of correlation matrix to judge the mode of dimension variation is also discussed. The max eigenvalue and it's eigenvector embodied the primary mode of dimension variation,which is caused by the primary reason which should be especially controlled. Finally,the approach of applying computer for analysis is pointed.