The problem of time and frequency synchronization is a bottleneck technology for the passive SAR system with spaceborne illuminators. In order to analyze the impact of time and frequency synchronization error to passive SAR imaging, the mechanism of time and frequency synchronization error was studied based on the particular operation mode of passive SAR. Then the error model of time and frequency synchronization was established, and the integrated error transfer model from synchronization error to passive SAR imaging was established. In the end, the correctness of the theoretical analysis was validated by simulation experiment. The theoretical analysis and the simulation result show the accuracy requirement of time and frequency synchronization for such a system. The conclusion can be used as principal guidance for passive SAR system design and synchronization method research.