The invention discloses a method for detecting serial digital quantity signals. An ASK circuit, RET circuits and a TER circuit are used by the method, wherein the ASK circuit is located at the head end of the circuit and used for sending an ASK signal; the RET circuits are distributed on the segmented serial circuit and used for collecting the digital quantity signals to be detected, coding the digital quantity signals according to protocol and sending out an RET signal; and the TER circuit is located at the tail end of the circuit and used for sending a TER signal. All the signals are transmitted on the serial circuit connected in a segmented manner, particularly, the ASK signals which are continuously sent out by the ASK circuit are received by the RET circuit, and then, the RET signal is sent out by the RET circuit, thus connecting the serial circuit in the segmented manner; after the RET signal returned by the RET circuit is received by the ASK circuit, the digital quantity signals and the relative position of the RET circuit in the RET signal are detected according to the predetermined protocol; and after the TER signal returned from the TER circuit is received by the ASK circuit, that the ASK signals reach the tail end of the serial circuit is judged. Accordingly, the entire process circulating continuously constitutes the method for detecting the digital quantity signals through the serial circuit.