Abstract: A new memory water cut meter system was developed in view of hydraulic pump well can’t be testing water cut through annular, this system was composed by down-hole testing meter, sampler shell of hydraulic pump, anti-vibrator, data interface of surface playback, portable computer and testing software. Testing instrument was installed in sampler at heel of hydraulic pump, put into down-hole with pump, and it can examine water cut of formation fluid, save history curves in real time by data memory. The design of instrument realized micro-miniaturization, the sensor, detecting circuit, thermal compensation and software process using real-time processing calibration, effectively improved water cut testing resolution and accuracy.