Software quality evaluation is complicated, and the major existing evaluation methods are too subjective in weight setting. In this paper, a synthesized evaluation method based on rough set theory is presented. This method converts the weight determination of fuzzy synthesized evaluation into the calculation of the importance of attributes in rough set theory. The weight is completely determined from the law of the data, to avoid the randomness of subjective method and the uncertainty of objective weighting method. An example shows this method is effective and feasible.