With the wide applications of the global navigation satellite system, the security problem of it has gradually become the focus of attention. In order to detect the induced spoofing, the most covert spoofing technology for satellite navigation systems, a combo-signal model which processes two satellite navigation signals simultaneously was proposed. Based on this signal-processing model, a method to detect induced spoofing signals was proposed. Then the detection threshold of the method was analyzed. An experiment with the BeiDou B1I and B1C signals and a software receiver implementing this combo-signal model was used to verify this method. The experimental results show that this method can effectively detect the induced spoofing. The statistics of the detection probability are consistent with the analysis.