Optical modulation theory of DE-MZM on board satellite was studied, output optics field expression of modulator with single input microwave signal was obtained. The analytical expression of four key parameters including carrier to noise ratio(CNR), RF gain, noise figure(NF), spurious-free dynamic range(SFDR) were deduced. The inter-satellite links transmission equation of microwave photonics was built. Using simulation software of OptiSystem, simulated model of microwave photonics links on board satellite was constructed and simulating research was performed. The simulated results show when the bias point is set to orthogonal bias point, RF gain is optimal. CNR, NF and SFDF are synchronously optimized when the modulator is low biased.