The intermodulation distortion greatly deteriorates the receiver sensitivity of intersatellite microwave photonics link in the range of high input signal power. The situation of N quadrature phase shift keying (QPSK) modulation signal input is considered and the intensity modulation/direct detection (IM/DD) intersatellite microwave photonics link model is presented. An exact analytical solution for any harmonic and intermodulation components of receiver signal is deduced with the method of Fourier expansion, Fourier transform/inverse Fourier transform and Graf addition theory. Combined with the number of third-order intermodulation distortion, the relationship formula between receiver optical power and signal-to-noise and distortion ratio (SNDR) is derived. The analysis concentrates on the relationship between receiver sensitivity of intersatellite microwave photonic link and the number of channels, the modulation index under different modulation modes. When the modulation index is small, the receiver sensitivity is robust against the change of channel number. The receiver sensitivity increases and then decreases as the increase in modulation index. It shows that an optimum modulation index can maximize the receiver sensitivity of link.