An optimized data compression method of freeformed NURBS surfaces based on the differential data of  coordinates of the control points is improved from the model of freeformed curves and surfaces described by the NURBS method. Discrete cosine transform (DCT) is applied to the differential data matrix of coordinates of the control points associated with weights and then quantization compression is carried out in the optimized data compression method. Accumulated errors of the recovered data generated from data compression are transferred together with the compressed data in addition to the high efficiency of data compression. Finally,it is proved the data compression method is effective and useful by comparing the  recovered picture with the original one in an example.