This paper researches the theory of multi-probes EST (Error Separation Technique) further. The computer simulation on the three-probes EST is also carried out. Several contrastive experiments of the on-line measurement are carried out in a grinding machine (MB1332A). The workpieces used in the experiments had been measured by TALYROND 262 Geometrical Error Measurement Instrument. The results of these experiments successfully verify that the theory and mathematical models of this paper are correct. The contrast of the measuring results in these experiments proves that the three-probes method can realize the complete separation of all kinds of errors basically and this method is applicable to on-line measurement of a workpiece and it can also make the measurement accuracy very high.