Abstract: At present,there is a lack of method in the internal software of coordinate measuring machine(CMM)to deal with the error data,as a result,the evaluation is influenced.To solve the problem above,methods for excluding error data are discussed in this article based on probability theory and mathematical statistics.Then the least square method for calculating plane uncertainty is analyzed and details in data processing based on the least-squares fitting methods are described. At last an example is given to verify the program.The results show that the schemes discussed in this paper are feasible and have certain application prospects in CMM.