Abstract: Aeromagnetic data downward continuation to sea level instead of marine magnetic survey data can improve use capability of survey data. Based on principle of multiscale edge detection, a new method to improve accuracy of aeromagnetic data downward continuation to sea level is studied in this paper, multicale edge constraint iteration method is presented. By the calculation, it is shown that the new algorithm can improve accuracy of downward continuation, accord with accuracy specification of three or four level marine magnetic survey