Flexible loop closing using single-core asymmetric phase shifting transformer (SAPST) can improve the success rate of traditional distribution network loop closures. However, the complex structure and intrinsic characteristics of SAPST increase the complexity of configuring protection devices, which may lead to malfunction or failure of protection actions and reduce protection sensitivity. To address these issues, an adaptive current protection method for loop closing networks employing SAPST is proposed. First, an equivalent model of the loop closing network containing SAPST is established, and the mechanism by which SAPST affects traditional current protection is analyzed. Then, based on the SAPST tap position information, a stage-I protection scheme is developed by calculating the short-circuit current using the fault compound sequence component relationships. A stage-II protection scheme is established by adjusting the branch coefficients. Additionally, switching criteria for protection schemes are designed to evaluate the loop closing status in real-time, and a flowchart for the loop closing protection scheme is proposed. Finally, the proposed protection scheme is verified using PSCAD/EMTDC and the RTlab hardware-in-the-loop simulation platforms. Experimental results demonstrate that the proposed scheme offers high selectivity and reliability, providing theoretical support for the engineering application of SAPST.