The invention discloses a preprocessing method for deformation data of a panel of a reflector antenna. The method takes deformation data of the reflector antenna as a processing object, and selects different data preprocessing methods according to different data types in engineering of a sector panel sampling point three dimensional coordinate, a triangular unit nodal coordinate and a quadrilateral unit nodal coordinate; an area coordinate and a polar coordinate are introduced to simplify an integral domain of any unit; the efficiency of the numerical integration is improved by using the Gauss integral formula; the number of lobes of a directional diagram are evaluated by referring to the half power lobe width; the number of discrete points of each lobe are picked up to determine the discrete precision of the directional diagram; according to the discrete precision of the directional diagram, the numerical integration calculation is repeated, and a complete far field directional diagram of a deformed reflector antenna is drawn in the end. A simulation result shows that the invention can not only effectively reduce the data processing time, but also improve the calculating precision of the antenna directional diagram; thereby the preprocessing method can be applied to the preprocessing of the deformation data of the reflector antenna under a plurality of engineering situations.