To solve the problems of overexposure and tailing which were produced by non-ideal exposure control in the space image,an exposure control algorithm based on illumination change and flexible block segmentation was proposed. First,considering the influence of light radiation attenuation bringing by atmospheric absorption,the relationship between light intensity and exposure time of CCD was derived,and the imaging model of the space image was obtained; Secondly,in order to estimate the exposure condition of the last image,the last image was flexibly segmented,and the gray averages of two adjacent blocks were compared for judging whether the two blocks were combined. If the difference of the gray average is bigger than the threshold,the two blocks are combined,others else they are not. The exposure time can be estimated by the two methods. Experimental results indicate that the SNR of the space images increased with 2.49 dB. This algorithm can effectively inhibit the space image producing tailings and greatly reduce the phenomenon of overexposure.