The optimal placement of PMU exerts very important influences on the application of Synchronized Phasor Measurement Technique in power system. In the paper, the optimal placement of PMU is firstly transformed into importance evaluation for the node. Then, PMU optimization algorithm of power system is proposed based on property evaluation of information entropy in connection with node importance evaluation. In the main idea of the algorithm, PMU is configured respectively according to importance order of each node in power system. As the experimental results show, attribute of se becomes the most important one in the property evaluation of information entropy. Contrasting original score Table 1 with the evaluation results Table 7, we conclude that final importance order for the node brings into correspondence with the score of attribute se, which proves the correctness of the algorithm eventually. Two methods of optimal placement of PMU raised in the end provide very strong instructive significance to the practices in reality.