The performance of intersatellite microwave photonic link under synchronous modulation of multiple-frequency-band signals is different to the situation of single channel signal modulation. The link with synchronous modulation of four-channel signals of Ku and Ka bands is modeled. The radio-frequency signals received by satellite are optically processed such as amplification, transmission and distribution. The nonlinear components are analyzed with Bessel expansion, the signal-to-noise and distortion ratios (SNDRs) under single sideband (SSB), double-sideband (DSB) and push-pull modulation are derived. The link performances with different modulation are contrasted. The results show that, nonlinear distortion has a more serious effect on SSB modulation than DSB modulation. The optimal SNDR of SSB modulation is equal to that of DSB modulation and the corresponding modulation index of SSB is higher than that of DSB. Low bias of push-pull modulation cannot optimize the SNDR. Taking signal quality and power into consideration, the intersatellite microwave photonic link under synchronous modulation of multiple-frequency-band signals should choose the DSB modulation.