Abstract: A line fault of a complex power grid with multi line DC and AC transmission in parallel can cause the mass shift of the active power, which may lead to the system fluctuation and grid disruption.A reasonable solution is given after the analysis of the relationship between the EDCPS and reactive power control. When a fault occurrs in one of the DC lines in parallel, the voltage stability is improved by the reactive power coordination control system of the nearly convertor station, as well as the emergency DC power support of other DC lines. A hybrid power system with one AC and three DC lines in parallel is created in PSCAD/EMTDC.Simulation results show that this strategy can significantly improve the frequency and voltage stability, and it is available to the actual system.