This paper studies how to balance the accuracy of the calculation with the speed of the solution, as the number of freedom degrees is large and the temperature distribution cannot be obtained quickly when applying the traditional solution method of numerical calculation for the temperature distribution of the microwave heating medium process. For this reason, on the one hand, this paper derives a set of higher-order non-linear equations in finite element discrete format for the microwave heating model, and constructs a snapshot matrix. On the basis of this, the optimal proper orthogonal decomposition(POD) basis is obtained by introducing the POD method, which further reduces the dimensionality to obtain the low-order microwave heating discrete control equations. On the other hand, an expression for the explicit dissipated power inside the medium in a rectangular waveguide under TE₁₀ mode wave radiation is developed, and an effective calculation of the global temperature distribution of the microwave heated medium is carried out. The numerical results show that the proposed method based on the POD can accurately calculate the temperature distribution inside the medium during the microwave heating process, and the computational speed is increased by 82.9% sim 85.5%. At the same time, the method has the feature of not having to recalculate the POD basis when the heating boundary conditions or initial conditions change, and can describe the super 99.9% energy in the higher order model with less basis, which is very important for real-time control and fast calculation of the temperature distribution of the microwave heating medium process.