The invention relates to an RTDS-based distribution testing system of a distributed network. A simulation interface subsystem is connected with an RTDS device to realize acquisition of small voltages outputted by the RTDS and the input/output of switching values. Each of a plurality of simulation terminals is connected with a corresponding distribution terminal to simulate a high-voltage transformer to output a secondary voltage and a secondary current and simulate a high-voltage switch to output a position signal, and collect tripping and opening-closing switching values of the distribution terminals. The simulation interface subsystem and all the simulation terminals carry out data interaction by wireless transmission. On the basis of the RTDS, the output function of the simulation data is distributed to a plurality of synchronous-operation simulation terminals, and each simulation terminal is arranged at the installation position of the distribution terminal. On the one hand, simulation data from the RTDS are received and outputted; and on the other hand, response information of a to-be-tested distribution terminal is received and is fed back to the RTDS, thereby realizing closed-loop testing of a distribution automation system under a real-time communication network impact.