Soft open point (SOP) can flexibly control the active and reactive power, realize the flexible closed-loop operation of the distribution network, and greatly improve the flexible and optimal operation of the distribution network. Aiming at the problem that the current SOP optimization operation capability analysis is not comprehensive, this paper proposes an evaluation method for the capability of SOP to support the distribution network optimization operation. Firstly, the topology structure of SOP and control strategies under different operation modes are introduced, and a quantitative analysis model of SOP supporting the optimal operation effect of distribution network is established, including optimizing network loss, balancing feeder loads, and promoting distributed renewable energy consumption. Combined with an actual flexible interconnection project Dongguan distribution network, a case study is carried out, the optimal operation effect of SOP is quantitatively analyzed, and its key influencing factors are pointed out, which can provide useful ideas for distribution network planning and operation.