Multiple frequency microwave signals can be modulated into optical field simultaneously with microwave photonic technology on board satellite.Therefore data may be processed at high speed on-board and transmitted over long distances between t wo satellites. When multi-frequency band microwave signals are modulated,the inter-modulatio n distortion is one of the important factors which affect the optical transmission performance o f multiple frequency bands microwave signals.The Optical modulating method of on board dual -frequency bands microwave signals with two channels in each frequency band is researched.Severa l orders of harmonics and inter-modulation distortion terms are analyzed.Expressions of ou tput signal to noise distortion ratio (SNDR) are deduced.Optimized DC bias p hase and modulation index are calculated, which guarantee the optimized output SNDR.Simulated mode ls are built up based on simulated software of OptiSystem.Research results show that nonlinear inter-modulation pr oducts of Ku include the third-order inter-modulation distortion (IMD3) of Ku,IMD3and the second -order inter-modulation distortion (IMD2) between two frequency bands;Nonlinear inter -modulation products of Ka include IMD3of Ka,IMD2of Ku,the second harmonic distortion (H D2) of Ku and IMD3between two frequency bands.Simulated results show that when modulation index is 0.17, DC bias phase is 0.535π,and optimized SNDR of Ku freque ncy band is 21.50dB.When modulation index is 0.22,DC bias phase is 0.525π,and optimized SNDR of Ka frequency band is 15.32dB.