The theoretical expressions for the power before and after imaging processing of non-coherent jamming, 1D convolution jamming and 2D coherent jamming against synthetic aperture radar (SAR) is deduced, and the imaging process gain(IPG) model and the interference-signal power rate (ISR) about SAR system parameters and jamming areas are established. The theoretical analysis results demonstrate that to a certain extent, the IPG and ISR of coherent jamming decrease as the jamming area increases, and that if the interference region range width of the 1D convolution jamming is greater than the range resolution before SAR imaging, its IPG and ISR are the same as that of non-coherent jamming, and the results also show that if the interference region range width and azimuth length of the 2D coherent jamming are greater than the range resolution and azimuth resolution before SAR imaging, the ratio of IPG and ISR between it and non-coherent is equal to the azimuth over-sampling ratio. Simulation corroborates the availability of theoretical analysis results and conclusion.