When we apply constant values of SOS and DC in reconstruction, the in-focus region will be in a certain depth, causing artifacts and displacement at other depths which deteriorates the image quality seriously. In this paper, the detailed reasons are analyzed for this phenomenon and. Furthermore, a reconstruction approach based on Fitted Delay Compensation (FDC) is proposed. It uses the various fitted delay compensation in image reconstruction, other than apply fixed delay and can significantly reduce the artifact. The experiment is carried out to validate its efficiency, which proves that, compared with the traditional reconstruction algorithm like delay and sum back projection (DNSBP), it shows pretty good effect in improving the image quality.