The outputs of adjacent wind farms have some correlation characteristics because of similar resource conditions, which has certain influences on transmission network expansion planning. In this paper, the influences of multi-wind power output correlations on transmission network expansion planning are considered. Firstly, the correlations between the outputs of adjacent wind farms are studied by Copula theory, and the method of generating wind farm samples with correlation is presented. Secondly, a transmission network expansion planning model is constructed based on the minimum cost method. In this model, Monte Carlo simulation technology is utilized to analyze uncertain characteristics of power flows resulted from multi wind farms that arc integrated into electric power grids simultaneously. At last, the simulation results based on the improved Garver 6 system verify the feasibility and rationality of the proposed model and algorithm. The results also show that the correlations of wind power outputs among multi-wind farm have a significant effect on the transmission network planning results, which should be taken into account in the planning.