Abstract: The communication quality of TWC (train-wayside communication) system directly affects the normal operation of lines. A quantitative detection method of TWC based on FSK signal is proposed. Through analyzing and calculating FSK signal, comparing and analyzing the parameters of voltage amplitude, waveform distortion and symbol error rate, the communication quality of wayside TWC system is estimated. The field test results of Shanghai Rail Transit Line 2 show that the method can detect one-way communication quality of trains at precise stop positioning in CTM (continuous transmission mode) and warn fault points, which helps to realize the quantitative analysis of TWC quality technical indicators, improving detection efficiency and fault treatment accuracy.