Abstract: The key point of using comprehensive evaluation method is the reasonable The key point of using the comprehensive evaluation method is the reasonable values of weights of the influencing factor, and different weights have great influence on the finial evaluation results. Although there are currently a lot of methods to confirm weights of influencing factors, these methods have some deficiencies. In order to overcome these deficiencies, a new study of weight back analysis method based on the optimization theory is suggested, which changes the directly given weight methods to the problem of back-analyzing the weights of the influencing factors according to engineering samples. A mathematical optimization model of the weight back analysis method is derived based on the extension theory and genetic algorithm, and the corresponding calculation program is compiled. This method is universal, shows a new idea and can be used in any weight problems. The solving process of the method is fully driven by engineering samples, and no experience is necessary, and it is very useful especially in the absence of expertise. Finally, the results of this method in practical engineering show that this method is reliable.