A method and apparatus for generating electricity and producing carbon and heat via biomass fixed bed gasification, said method and apparatus utilising medium calorific value combustible gas to satisfy high-temperature high-pressure boiler heat requirements, and increasing overall electricity generation efficiency. The method and apparatus have low nitrogen oxides amounts, satisfy environmental protection requirements, and do not require denitrification treatment. The method comprises the following steps: feeding a biomass raw material into a gasification apparatus to prepare a medium calorific value biomass combustible gas, and performing gasification on the biomass raw material at 700-850° C. under the effect of an air/water vapour pre-mixed gasification agent to produce a combustible gas, the calorific value of the combustible gas being 1600-1800 kcal, the temperature being 200-300° C.; directly feeding the combustible gas into an environmentally friendly combustion chamber for combustion, and then into a high-temperature high-pressure boiler, the gas combusting within the high-temperature high-pressure boiler to produce high-temperature high-pressure steam, which drives a steam turbine to generate electricity; utilising steam waste heat discharged by the steam turbine; using boiler tail gas to heat air by means of an air preheater, the hot air being respectively fed into the combustion chamber and the gasification apparatus by means of an air blower, and utilising the waste heat.