Abstract: In order to explore how to avoid Braess paradox when adding transmission lines in interconnected power grid, this study uses the second order Kuramoto-like model to model the dynamics of the power grid, and connects the subnets through the largest nodes to construct interconnected power grid. When there is power transmission between the two subnets, consider adding transmission lines inside and between subnets to explore the probability of Braess paradox in interconnected power grid and analyze its reasons. The results show that the probability of Braess paradox is related to the transmission power between the subnets. When the power between subnets reaches a critical value, adding transmission lines in the power receiving subnet or between two subnets, the probability of Braess paradox in interconnected power grid will be reduced to nearly zero. Therefore, the Braess paradox phenomenon should be avoided. The reasons for this phenomenon are analyzed in this paper.