Abstract: Using an isolated system in Huolinhe as an example,the access mode of wind power plant to system by flexible DC mode is proposed to reduce the system voltage fluctuation and improve system voltage stability. In Flexible DC power transmission mode, voltage source converter has directional characteristics, and the decoupling of active power and reactive power is realized by using pulse width modulation technology, which can be achieved in an independently continuous way. At first, the steady power flow calculation is carried out by using of systems with different power transmission modes and different grid-connected capacities, and the voltage level on load nodes can maintain within stable range. Then, transient state of system is simulated under such fault cases as the conventional generator fault, load fault and line fault in the system, and voltage fluctuation is also maintained within the allowable range, and can stabilize quickly without the adoption of control measures. The results of the simulation show that wind farm can be connected to system by flexible DC power transmission technology, and the stability of system voltage can be improved greatly by comparing with that by conventional AC transmission.