Abstract: The investment control index of feasibility study has an important role in estimating the investment of power grid, calculating the cost of preliminary work and auditing the investment of the project. To promote the precision of the investment control index of substations and make that index practical, this paper applies the modularization design concept to measure and calculate the investment of substations on feasibility study. The result show that: the modularization design concept could be applied into achieving the accuracy of the predictions.