The measuring precision of error separation technology is directly related to error separation parameters selection. If the parameter selection rules aren’t followed correctly, the accuracy of error separation will be affected badly, and even the error figure got will be a distortion result. Through a discussion on the characters of error separation technology, eight rules for choosing error separation parameters of multi-probe method are made in this paper. These rules are regarded as the general laws to follow when measuring the geometrical error by multi-probe method. Based on the results of the online measurement experiment, the parameter selection rules are proved to be effective.