For grid-connected microgrid, this paper proposes an evaluation index system, which contains reliability, autonomy, regulation of interactive power, environment-friendly degree and utilization of tie-line and renewable energy, and then translates them into the form of constraint. In conjunction with the output characteristic of distributed generators, and taking the lowest total cost as objective function, it constructs the optimal planning model of microgrid. Based on the real data of load and meteorological, this paper analyzes the effect of index constraints to capacity allocation of microgrid, and the relationship between different indicators. The results show that the index system improves the rationality of the optimized allocation and enhances the flexibility of the optimization model, meeting the diversification demand of users. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015A050104).