The invention discloses an inherent detection method for a PNC (physical-layer network coding) continuous phase modulation signal. The method solves a problem that a relay node receives two overlapped signals with an unknown carrier phase difference through the memory characteristics of a continuous phase modulation signal. The method comprises the following steps: firstly defining an inherent detection judgment quantity of a to-be-detected code element of the relay node according to the criteria of maximum likelihood ratio; secondly calculating the conditional probability of receiving a signal in a plurality of code element time periods, carrying out the averaging of the carrier phase difference, phase state and other code element sequence combinations in the conditional probability, and designing a front-end filter; finally enabling a baseband signal to pass through a matching filter, and selecting the information, which enables the judgment quantity to be maximum, as an output result. The method can effectively eliminate the impact on the relay detection performance from the random phase error of carriers, and is excellent in detection performance. With the increasing of the length of an observation window, the performance is remarkably improved, and gradually approaches the optimal coherent detection performance.