Abstract: In some space project, a specific CCD sensor has been used to design a set of space imaging CCD camera system, and the image frame rate is higher than the standard frame rate of CCD sensor. Signal to noise ratio should be decreased by simple overclocking readout the CCD. Firstly, a variety of reasons which could affect the imaging signal to noise ratio of CCD camera under the space conditions were analyzed, it had been found that readout noise was the most important reason. So the regional frequency doubling readout methods was introduced and used to improve the output frame rate of CCD camera. Namely, four times the pixel clock was used to readout part of CCD pixels in the horizontal and vertical directions. Finally, the SNR of image signal by regional frequency doubling readout CCD and overclocking readout CCD was compared. Test result shows that the former image has higher SNR.