In order to explore the characteristics of the servo control system of wire cut electrical discharge machining (WEDM), based on the threshold voltage threshold control method, the WEDM servo control system platform was built on the basis of the middlespeed WEDM. The frequency signal collected during discharge was analyzed and processed by using FPGA chip,and the servo motion was carried out according to the processed signal. The relationship between the cutting efficiency and the servo control system characteristics of WEDM was explored by experiments, and the influences of the threshold and detection period on the machining efficiency were obtained; through verification experiments and analyzing discharge status ratio, the optimal threshold value was explored. The results show that when the detection period is 0.5 s, high machining efficiency can be achieved; when the acceleration area accounts for 15% and the uniform speed area accounts for 62%, higher machining efficiency can be obtained too.