The measurement uncertainty of microwave power was evaluated by Monte Carlo method (MCM). The evaluation process of measurement uncertainty was introduced with MCM, and procedure of MCM with MATLAB was given. Both single batch MCM and adaptive MCM method were used to evaluate measurement uncertainty of microwave power at a given frequency. The results from two MCM were compared with GUM method. It showed that the results were almost identical, addition to 5% deviation in standard uncertainty between MCM and GUM. The MCM validated GUM and was fully fit for evaluation measurement uncertainty of microwave power. The MCM can deal with linear model perfectly, and its advantage is obvious in the case of similar components of uncertainty, and it is simple, convenient, and easy to spread at same time.