With the large-scale access of distributed generation (DG) to the distribution network, the traditional distribution network with limited regulation ability often has problems such as node voltage over-limit and bidirectional power flow. Soft open point (SOP) with excellent power flow control ability is one of the devices to adapt to the new distribution network, but the high cost makes it necessary to optimize the location and capacity. In this paper, a two-step SOP location and capacity method based on power flow betweenness is proposed. Firstly, the power flow betweenness suitable for power network characteristics is proposed, and then the SOP location strategy based on power flow betweenness is analyzed. Then, taking the lowest annual comprehensive cost as the objective function, the SOP constant volume optimization model is established and solved by the second-order cone programming algorithm. Finally, the IEEE33 node example is used to verify the proposed method. The results show that the proposed SOP location and capacity determination method can effectively reduce the annual comprehensive operation cost of the distribution network.