The invention relates to a power grid voltage rapid assessment method and system. The method comprises the following steps of firstly, designing a wind-solar-electricity output scene with a uniform coverage range; and then obtaining the output data corresponding to the inputted wind-solar-electricity output scene data, performing polynomial sparsification to obtain a sparse polynomial chaotic expansion model, and finally substituting the wind-solar-electricity output data to be assessed into the sparse polynomial chaotic expansion model to obtain a rapid power grid voltage assessment result. The method aims at the problem of power grid safe and stable operation assessment, and improves the efficiency of the power grid voltage safe and stable margin rapid assessment considering operation uncertainty. According to the assessment method, a fitting model is established by adopting a data driving method in power system safety risk assessment to replace a traditional continuous power flow model for solving the voltage stability of the system, so that the calculation efficiency is improved, and meanwhile, the model has relatively better regression precision and relatively higher accuracyin voltage stability calculation of a to-be-assessed power grid scene.