As a typical application of cyber-physical system, smart power grid is composed of interdependent power grid and communication/control networks. In order to simulate the actual cyber-physical power grid, we propose a novel modeling method based on DC power flow model. In our model, each communication node is supported by only one power node, while each power node is monitored and controlled by k communication nodes. Each communication node controls no more than n power nodes. We show that the system controlling cost is proportional to k. With numerical simulation, we study the relations between load loss (L-loss) of power network and the failure ratio of communication edges (p). When p is small, with the increase of k, the robustness is greatly improved. However, the effects are not obvious with continuing increasing k when k approaches to 4. However, when p is big, opposite results can be obtained. This indicates that increasing cost without limit is not always a better choice.