Part I: This article first the development situation and the significance which evaluated to flatness error has carried on the elaboration, then briefly introduced flatness error measuring technique, had the light wave interference method, node distance the law, the standard plate hit the table law, the light scanning method, elaborated their survey principle and has the related graph explanation. This article evaluated the method to the flatness error four kinds also to carry on the elaboration, had the smallest condition law, the triangle law, the diagonal process, the best square approached the law, and separately had pointed out their good and bad points and were suitable the condition. Simultaneously simply introduced the revolving method and its suitable condition, the article main utilization basic plane law.