This paper proposes a new type of rainfall retrieval algorithm, which improves the method using the Volterra integral equation (VIE). The proposed algorithm makes pre-analysis on the data received by synthetic aperture radar to get information such as the rainfall start point and the scope of the rain. The VIE retrieval algorithm is then applied in a short distance to get information of the rain distribution. Further analysis is then made on the information obtained in the previous step to find parameters such as shape of the rain and the rain rate. According to the most commonly studied rainfall distributions that are symmetric, the rainfall distribution is obtained. Simulation results show that the proposed algorithm is effective and efficient, with high accuracy.