The measurement of spool valve overlap value of a servo valve is a ke y processing technique of servo valve manufacturing. This paper introduced the m ain method of overlap value measurement, including indirect measurement, pneumat ic general measurement and hydraulic general measurement. The principles and mat hematic models of these methods were presented, and the merits, the demerits, an d the application methods were analyzed. For the changing of discharge coefficie nt may decrease the precision of general hydraulic measurement, a compensation m ethod based on the orifice flow pattern was proposed, which could increase the measurement precision of overlap value.