Aiming at the problem that the dual-channel configuration of the traditional GNSS-R (global navigation satellite system-reflected) passive radar system has a large amount of computation in signal processing and a high hardware cost in engineering implementation, a blind detection method of the weak target echo of single-channel GNSS-R passive radar based on higher-order cyclic cumulant was presented. Strong direct wave signal was extracted from the single-channel mixed signal using the principal component analysis method. Higher-order cyclic frequency of weak target echo was estimated by higher-order cyclic frequency of direct wave signal. Weak echo signal was extracted from the single-channel mixed signal based on its different characteristics of higher-order cyclic frequency from other signals, so that the object detection was realized by matched filtering. Simulation results show that the proposed method can effectively extract the weak target echo without prior information, and has better target detection performance compared with the traditional two-dimensional matched filter target detection method.