Abstract:  ViSAR（video synthetic aperture radar），as a microwave remote sensing system，which can continuously monitor time-sensitive targets in the significant region in camera mode，has attracted more and more attention，but the analysis of video imaging capability of video SAR system is not thorough enough.Based on the SAR echo and the system parameters，a space-borne ViSAR imaging capacity model was presented，which can be used in the analysis of space-borne SAR potential application of video imaging.The X-band and Ka-band ViSAR parameters were used to simulate the SAR system video imaging capacity.With the same frame rate of ViSAR，the higher the frequency of the ViSAR system，the easier it is to form a SAR video with an independent frame rate；with the same azimuth resolution of ViSAR system，the larger the central squint angle，the greater the required ratio of the ViSAR overlapped sub-aperture.The research can support spaceborne ViSAR system design theoretically.

Key words: video synthetic aperture radar, space-borne SAR system, time-sensitive target, continued monitor, video imaging