This paper develops an aggregation-based algebraic multi-grid (AbAMG) method to efficiently analyze the power grids. Different from the conventional algebraic multigrid (AMG) scheme, an innovative constructing method of global inter-grid mapping operator is employed to not only enhance the sparsity of coarse grid operator for reducing the computational complexity but also solve the problem with better convergent rate. The proposed method can solve the circuit with size over two millions in 167.6 CPU seconds (including DC analysis, and transient analysis with 50 time steps), and the maximum error is less than 1%. The significant runtime improvement, over 26X faster than the Induct-Wise [1] and over 1.25X faster than the conventional AMG method, and less memory usage, 40%of the memory usage in [1] are demonstrated.