Abstract: The multiple-state fault model of wind turbine is built by considering its running,outage and derating state,and the output power of wind turbine is evaluated probabilistically using Monte Carlo method to get the samples of wind turbine state and wind speed based on the influence of the randomness of wind speed and fault rate on the output power of wind turbine.Then the algorithm of probabilistic assessment of the output power of wind turbine is realized by Matlab,the output power of 1.5MW series wind turbine in one wind farm is evaluated,and the probability values under different output power state of this type wind turbine are given,which verify the effectiveness and adaptability of the proposed model and assessment method.