The reliability of railway signal relay will greatly affect the stability and reliability of the communication system. By using the railway signal relay as the sample, the high speed-data acquisition of the relay contact voltage, coil current and coil voltage was completed.In order to remove the noise interference,the collected data were analyzed by frequency spectrum and filter filtering. Based on the principle of electromagnetic mechanism of electromagnetic relay, the mechanism of the second time close was analyzed, and the calculation method of close time t6 was studied, then the time parameters of relay were obtained. In addition, the relationship between time parameters and relay reliability was described. The accuracy of the test system was proved meet the design requirement by compared with the measured data.