The invention relates to a fuel gas preparation method and fuel gas preparation apparatus. The fuel gas preparation method comprises the following steps: sending powdery solid fuel and a gasification agent into a gas production chamber of a gas production furnace to perform a reaction for generating high-temperature combustible gas and high-temperature ash; enabling the high-temperature combustible gas and high-temperature ash generated by the reaction to pass through a first heat exchanger for recycling a part of heat; sending the combustible gas which contains the ash and passes through the first heat exchanger into a separating device for removing the ash granules in the combustible gas, wherein the separated combustible gas is discharged from a combustible gas outlet of the separating device and the ash granules enter an ash collecting chamber of the separating device and is discharged from an ash outlet; and sending the combustible gas discharged from the separating device into a second heat exchanger for recycling heat. The fuel gas preparation method and fuel gas preparation apparatus provided by the invention can effectively recycle the sensible heat of the high-temperature combustible gas, increase the heat utilization rate of the system, solve the problems of ash deposition and wear in the second heat exchanger, and further increase the utilization rate of residual carbon in the ash.