This study aims to solve the problems of packaging materials and microwave input power selection in microwave reheating cold chain food. COMSOL Multiphysics 5.6 was used to establish the microwave reheating model of quick-frozen food. The four kinds of common quick-frozen food outer packaging materials were simulated, and a quick-frozen mashed potato with an initial temperature of −18 ℃ was reheated to 65 ℃ by microwave under 800 W power. The temperature and time rate curves of the center of the block and the temperature distribution of the cross section when the material reached the target temperature were studied. Then on this basis, the single variable of packaging material was controlled to change the input power and material shape respectively. The time for the four materials of meal box packaging to reach 65 ℃ was:447 s, 10 s, 525 s and 464 s. When the target temperature was reached, the material temperature difference of PP plastic packaging material is the smallest (5 ℃), and the material temperature difference of diamond column shape was the smallest (7 ℃). Achieving the target temperature at 6 kW microwave power consumes the least power (0.195 kW.h). The packaging material made of aluminum foil has the fastest microwave heating rate, the packaging material made of PP plastic has the best heating uniformity, and the materials in the shape of diamond column has the best uniformity during microwave heating. The heating benefit is the largest when the input power is 6 kW.