Abstract: At present, the judgment of characteristic parameters of opening pressure, closing pressure and pressure fluctuation value of safety valve are all summarized by test personnel according to experience. The accuracy of these data should be verified. In view of the problem, the paper proposed a new automatic data collection and processing method suited for characteristic experiment of safety valve with small flow. It analyzed overflow process of small flow by taking plunger type safety valve as example, gave diagram of hydraulic system used in the experiment, and introduced design and implementation of the data collection and processing software in details. The experiment result showed that the method can directly measure characteristic parameters of opening pressure, closing pressure, maximum pressure, minimum pressure and pressure fluctuation value in overflow process of safety valve, and can automatically judge whether these data accord with demands of the standard of MT419－1995 the valve for hydraulic support. It has features of simple operation and interface humanization.