A multifunctional air purifying device for removing indoor pollution by a thermal decomposition method comprises an air treatment unit and an air collection heater. The air collection heater is provided with an infrared lamp tube and an ultraviolet lamp tube. An annular water tank is arranged on an inner side of the upper part of the air treatment unit. A filter screen runs through the annular water tank and is connected with an air cap, and a fan is provided at a joint between the filter screen and the air cap. The filter screen includes an early effect filter screen, a HEPA filter screen, an activated carbon filter screen and a cold catalyst filter arranged in that order from a bottom to a top. A humidifier connects the annular sink and a nozzle located at an exhaust port.