Microgrid technology has been increasingly concerned for its high efficiency and environmental integration of various distributed generation (DG) units into large power grid system. The wide application of micro-grid system should consider the economy, and the economic evaluation depends on the system cost. The cost of microgrid system covers the investment, operation and maintenance cost of all GD units, and the power losses of microgrid system. The power losses cost, especially for 3 typical topological structure, was compared to determine the microgrid layout solutions based on topological structure and unit location selection. MATPOWER simulation software was introduced to calculate the power flow in different location of microgrid to get the power loss cost. The results show that the economic cost of microgrid system depends on its topological structure; the location of DG units has effect on the economic analysis of the microgrid system for the same topological structure. The microgrid with dual-grid integrated ring structure is of the lowest cost, and that with radial topology is of the highest cost.