In order to improve the voltage unbalance of large-scale wind power collection grid three-phase and solve the problem that negative sequence voltage unbalance factor exceeds the national standard, which sometimes even causes the wind turbine generators to be off grid, this paper proposes a split-phase flow optimization method that uses the split-phase reactive power compensation equipments in wind farms collected area to improve the voltage unbalance. Firstly, this paper takes the collection grid and the wind farms as optimization nodes, establishes an optimization model to minimize the mean value of voltage unbalance degree, then the node voltage safety constraint and the constraint condition of the reactive power compensation capacity of each phase of the reactive power compensation equipments are considered. Secondly, this paper introduces PSO to solve the optimization problem. Finally, an actual area wind farms collected is used to verify that the method proposed in this paper can effectively solve the problem that voltage unbalance degree is too high.