For the problems of the leakage and abrasion caused by pressure difference of traditional gear flowmeter, a non-pressure-difference and high precision flow measuring system was designed. Based on the LVDT’ s signal processor chip AD698 and STM32F407VGT6 microcontroller, the hardware circuits of processing the LVDT’ s signal, power supply conversion, motor driving and communication interface and so on were designed. On the base of digital PID, the control algorithm of the motor speed following flow and the flow measuring system software were developed. The high precision experiment platform was set up to realize non-pressure-difference measurement. The results show that: the system with the functions of feedback and control of the pressure difference can adjust the pressure difference between the entrance and exit, non-pressure-difference measurement is realized, the inside leakage of the flowmeter is reduced, and it has high measuring accuracy. Its relative error is less than 0.5%, which can satisfy the requirement of high precision flow measuring.