Digital mosaic technology is a common method used in digital image processing, but it is not good enough in SAR image inlay because the(geometric and radiation) distortion of SAR images is related to the direction and distance of radar beam. When the neighbouring image strips were inlaid, the obvious difference between them in tone and geometric position appeared. In this paper it will be found that the problem in digital mosaic of SAR images was solved. The mathematic theory of SAR image radiation correction and geometric correction was discussed in detail, and the effectiveness of the correction methods was approved by examples. The mosaic images with uniform tone and accurate position can be obtained after the suitable radiation correction and geometric correction for SAR images.