The invention belongs to the technical field of power systems, and provides a probability calculation method of power system quiescent voltage stability based on a load margin index on the premise ofconsidering wind power output randomness. The method comprises the steps of: selecting a load margin index to measure the quiescent voltage stability of the power system; calculating the load margin of each load node, and further calculating a system load margin according to the load margin of each load node; deriving a sensitivity relationship between the load margin of each load node and the injection power of a wind power node; and utilizing a semi-invariant method and Gram-Charlier series expansion, calculating probability distribution of the load margin of each load node through wind power probability distribution, and evaluating the quiescent voltage stability of each node. According to the method, the influence of the uncertainty of the wind power output on the quiescent voltage stability analysis is described, the quiescent voltage stability probability evaluation of the wind power grid-connected system is achieved, and the instability risk of the quiescent voltage stability isevaluated.