An operational method of crop yield disaster losses evaluation is introduced. In this method, crop yield loss rate are obtained by a novel method of division crop trend yield. Disaster losses of the area are assessed based on the data of some representing stations, thus samples numbers are enlarged. Crop sensitivity and climate vulnerability are considered in single disaster assessment model. The weights of various disasters are considered yet in the multifactor assessment model. This method is convenient and practical in operation application. Its estimate precision can meet accuracy requirements of operation application.