In order to study the influence of wind power, photovoltaic and load uncertainty on power supply capacity of microgrid, the paper combines the prediction error probability distribution of wind power、photovoltaic and load with Monte-Carlo samping method to establish a short-term power supply capacity evaluation method of microgrid considering wind power, photovoltaic and load uncertainty. Firstly, a deterministic prediction of wind power, photovoltaic and load was carried out by means of autoregressive non-parametric method, and then the prediction error of wind power, photovoltaic and load was analyzed probabilistically. Secondly, the Monte-Carlo samping method is used to sample the prediction error models of wind power, photovoltaic and load, and combined with the deterministic prediction results of wind power, photovoltaic and load, the possible scenarios of the microgrid are obtained；Several evaluation indexes which can be used to quantify the power supply capacity are defined, and the evaluation index of the power supply capacity of the microgrid is calculated according to the optimal solution of each scenario of the microgrid. Finally, a microgrid is selected as an example to verify the proposed method, the results show that the method proposed in this paper can accurately reflect the power supply capacity of the microgrid under different weather types.