There are some applications of error separation technique in actual measurement. However there exists a series of theoretical and technical obstacles, and the error separation technique lacks the objective assessment. The further discussion about the character of error separation technique by multi-probe method is made in this paper and six criteria for precision measurement of error separation technique by multi-probe method is also advanced. That is, (1) The criterion for veracity of error separation; (2) The criterion for periodicity of combination signal; (3) The criterion for the remnant first-harmonic in combination signal; (4) The criterion for validity of error separation results; (5) The criterion for validity of probes’ fixing angles ; (6) The criterion for nonzero character of weight function. These criteria are significant for the objective evaluation of the measuring apparatus’ measurement precision, the validity of the sampling data, and the confidence level of error separation results. The validity of the measuring condition was proved by the online measurement experiment.