The characters testing platform of the proportional flow valve is built, according to the principle of a method of air charging and discharging in an isothermal container. By using the method of approximation formula of mass flow in small hole in addition with the multi-term modification to process curve fitting to the experimental characters curves acquired by testing, the experimental model was built to describe the characters of proportional servo valve. The testing method and device described were simple with low testing costs. The built experimental model is already applied in the active control system for vibration reducer with good control effects.