Microwave heating is a promising technology in coal processing and coal seam permeability enhancement. It is vital to investigate the influencing factors for microwave heating of coal to ensure the optimal heating effect and the best energy efficiency. To address this, different types of coal samples with various water saturation were treated with various microwave powers and irradiation times. Thermocouple and infrared thermal image system were used to measure the temperature of coal samples during and after microwave treatment. Through analysing the temperature, the effects of dielectric property and water saturation of coal, microwave power and treatment time on microwave heating were investigated. It was found the heating rate of coal samples increases with the loss factor at the initial heating period, which then changes as the composition changes under microwave irradiation. It was also found that coal samples with low water saturation have much better microwave heating effects. Moisture not only impedes microwave heating but also facilitates uniformed heating, which impedes the formation of thermal fractures. Additionally, the experiment results suggest the average temperature increases with microwave power and irradiation time. However, extending the microwave irradiation time is more effective when the microwave power increases to a certain extent.