Abstract: The push-pull DC auto-transformer (PPDAT) has high power transmission efficiency, whereas it does not have the capability of electrical isolation. Although existing technologies such as DC circuit breaker or full bridge sub-module can isolate dc faults, they are costly. To reduce the cost of dc fault isolation, this paper studies the DC fault isolation strategy of PPDAT. Firstly, the topology and working principle of PPDAT are introduced. By analyzing the operating characteristics of four-winding transformer, the relationship between port voltage and bridge arm output voltage of PPDAT is deduced and established. Then, based on the analysis results of DC fault response characteristics, the PPDAT equipped with DC fault isolation component (DFIC) is proposed, and the corresponding dc fault isolation strategy is designed. When DC short circuit faults occur, PPDAT equipped with DFIC can quickly control the port voltage and block the fault current, so as to maintain the stable operation of non-fault DC system and reduce the equipment cost. Finally, based on PSCAD/EMTDC, the feasibility and effectiveness of the DC fault isolation strategy of PPDAT are verified, and the technical and economic efficiency of a variety of DC transformers with DC fault isolation capability is compared.