Because of compact size, light weight, low-cost, FMCW SAR develops rapidly in recent years with the rose of the small Unmanned Aerial Vehicle (UAV). However, the signal processing methods are very different from that of pulsed-SAR due to the invalid suppose of “stop and go” and hence it is some confused in the real-data processing. Therefore, it is significant to make a deep research of FMCW SAR. However, much attention is paid on the aspect of data focusing while little research concentrates on the raw data simulation, especially for moving targets. In view of these, this paper firstly derived an accurate 2-D spectrum model in the consideration of the in-pulses motion of FMCW SAR, and then a highly-efficient raw data simulation method for FMCW SAR with moving targets is proposed. Point targets and real scene raw data simulation experiments are carried out to validate it and the its efficiencyis analyzed, results show its highefficiency comparing with the conventional methods.