The invention relates to a high efficiency micro-discharge coal-fired hot water boiler. A smokeless chimney is installed with a low smoke discharging temperature, high thermal efficiency, a quick temperature elevating speed and high combustion efficiency. Since the chimney is smokeless, discharging indicators tend towards zero, so that effects of little burn, little discharge, scientific control,environmental protection and energy saving are implemented. The inventive boiler comprises a boiler body, one side of the boiler body is connected to a coal feeder, and the other side of the boiler body is connected to a fume channel waste heat recovery system which is connected to a desulfurization dust removing system. The boiler body comprises a combustion chamber, a chain grate is disposed under the combustion chamber, a main internal furnace and an accessorial internal furnace both of which are used as internal furnaces and communicate with each other are disposed above the combustion chamber sequentially, a water inlet is disposed on the main internal furnace, a hot water outlet and a smoke discharging pore are disposed on the accessorial internal furnace, and a fire averaging plateconnected with a boiler crown is disposed in the combustion chamber. Heat transfer steel tubes are disposed in the main internal furnace and the accessorial internal furnace, a set of heat transfer steel tubes used as fire path one is disposed in the main internal furnace, and two sets of heat transfer steel tubes used as fire path two and fire path three respectively are disposed in the accessorial internal furnace.