The invention relates to a coal gas, tar, semi-coke and steam poly-generation method based on a fluidized bed pyrolysis technology. The method comprises the following steps of: mixing coal and high-temperature semi-coke serving as a heat carrier in a fluidized bed pyrolysis furnace, heating, precipitating volatiles, and cooling and separating the volatiles to obtain tar and pyrolysis coal gas; discharging one part of semi-coke to obtain a semi-coke product, feeding the other part of semi-coke into a fluidized bed semi-coke heating furnace, performing combustion reaction with a small amount of fed air, heating all the fed semi-coke by using heat released after a small amount of semi-coke is combusted, feeding the heated semi-coke into a cyclone separator along with flue gas, and feeding the separated high-temperature semi-coke serving as the heat carrier into the fluidized bed pyrolysis furnace; and feeding the flue gas subjected to gas-solid separation into a complementary combustion waste heat boiler, completely combusting a small number of combustible components in the flue gas, producing steam, feeding into an air preheater to heat air required by combustion, removing dust by using a dust remover, and emptying. The method has the advantages of realizing the fractional conversion of the coal and improving the utilization efficiency and benefit of the coal.