Abstract: The site and time of wind farm construction are influenced by human and natural factors, which will impact on grid planning to a great extent. In view of the uncertainty of wind farm expansion, a probabilistic evaluation method for power grid planning is proposed. Firstly, the uncertainty of wind farm expansion is analyzed. Then the grid expansion probability, grid expansion cost expectation, flexibility of planning scheme regarding wind farm expansion are proposed, and the evaluation method based on bilevel stochastic grid expansion planning model is proposed. The case study verifies the effectiveness of the proposed indicators and method.