The invention provides a garbage pyrolyzing and incinerating harmless disposal system and a garbage pyrolyzing and incinerating harmless disposal method based on a pulverized coal boiler. The system is simple in structure, reasonable in design, convenient to use, environmental-friendly and high in safety coefficient. The system comprises a boiler furnace, a flue and a flue gas system connected successively as well as a drying and pyrolyzing device, a crushing and conveying device and a garbage combustor connected successively. A garbage crushing and sorting device and a feeder are successivelyarranged at an input end of the drying and pyrolyzing device, and the flue gas system is connected to an input end of the feeder; the flue gas system comprises a high-temperature flue gas pipeline and an intermediate temperature flue gas pipeline, the high-temperature flue gas pipeline is connected to the bottom of the pulverized coal boiler furnace to extract high temperature flue gas, and the intermediate flue gas pipeline is connected to a turning chamber of the pulverized coal boiler into an outlet flue of a coal saver to extract the intermediate temperature flue gas; and the garbage combustor is arranged between the lowermost pulverized coal combustor and an over fire air combustor of the boiler furnace.