The common phenomenon of open-loop operation of closed-loop designed distribution networks leads to a slow load transfer speed and unbalanced feeder power. Meanwhile, the increasing amount of DC loads and the growth of new permeability have brought new challenges to the operation control of distribution network, which requires stronger power flow regulation ability. This paper carries out the study of Soft Multi-state Open Point (SMOP) technology used in distribution network feeder in order to meet the aforementioned challenges. A topology of a four-terminal SMOP based on Double Clamp Sub-Module (DCSM) is proposed followed by its mathematical model analysis. Based on the mathematical model, the operating range of the proposed topology is then determined. After that, the structure of control system and a self-healing control strategy is designed for the SMOP. A four-terminal SMOP simulation model based on PSCAD/EMTDC is constructed in which the validity of the proposed topology and its control strategy are verified. This work is supported by National Key Research and Development Program of China (No. 2017YFB0903100) and Science and Technology Project of State Grid Corporation of China (No. 521104170043).