Abstract: In ground-based global navigation satellite system reflectometry (GNSS-R) power measurement applications, signal-receiving antennas could not perfectly suppress the co-polarized signal from backwards and the cross-polarized signal from both forwards and backwards.In order to analyze the influence of the antenna directivity on the correlation power of the target signals, a right hand circular polarized (RHCP) antenna and a left hand circular polarized (LHCP) antenna were used to receive the direct signal and reflected signal, respectively. The correlation power models of the signals received by the actual antennas were firstly established, and then the probability distribution and numerical characteristics of the actual signal correlation powers were determined successively. Based on simulating the numerical characteristics, the relative deviations and variation coefficients of the correlation powers were calculated and analyzed. Simulation results show that the actual antenna directivity can cause errors in the correlation power measurement of target signals. The RHCP antenna ’s directivity has a considerable impact on measuring the correlation power of direct target signal in the low elevation angle range, while the LHCP antenna ’s directivity significantly affects the measurement of reflected signal correlation power in entire elevation range.