Aiming at subjective weighting and objective weighting for the existing law, the respective advantages and disadvantages, put forward based on least square theory combination weighting method thinking. Spread function and the use of goal programming method to get the optimal combination weighting method the only existence theorems; use of advanced mathematics, linear algebra and other knowledge to prove the theorem of existence and uniqueness of optimal, and gives the combination weighting expression. The method of subjective and objective weight weighted weights together, so performance evaluation results will also reflect the subjective and objective conditions for the performance evaluation results of the reliability and accuracy of the foundation.