In order to limit the DC side fault current due to poles short-circuit of the Voltage Source Converters (VSC) DC side in DC distribution network, this paper studies the transient process of different stages during the DC side short circuit faults, and analyzes the protection scheme of AC Side Connecting Double Thyristors (ACDTS). Aiming at the problem that the current of ACDTS DC side is too large, this paper presents a way to improve the performance by making use of unidirectional thyristor, parallel resistance and inductance. The PSCAD/EMTDC is used to simulate the DC side fault of the improved ACDTS scheme, and compare with the traditional DC line fault and the DC side fault under the ACDTS protection scheme. The simulation results show that the improved ACDTS protection scheme can effectively limit the DC fault current. This work is supported by National Natural Science Foundation of China (No. 51607110) and Natural Science Foundation of Shanghai (No. 14ZR1417600).