A task risk assessment method combining variable weight theory with cloud model is proposed.Aiming at the deviation of the evaluation results caused by the extreme values that may appear in the task, the interval variable weight function is constructed, and the normalization standard of risk factor data is established.Aiming at the excessively strong influence of Ex in traditional cloud models on the assessment results in risk assessment, the interval form is adopted to weaken it, and the method for determining the digital features of the interval cloud model is improved based on the attribute mathematical theory.The rationality and effectiveness of the method are demonstrated through examples.