Abstract: Based on research of coal petrology and organic geochemistry,hydrocarbon-generating potiential of different coal micromacerals which separated from gas coal and fat coal of Longtan formation in the middle-southern area of Hunan province has been discussed.The study suggested that exinite was the best maceral for generating hydrocarbon,vitrinite took the second place.Both of them are major hydrocarbon-generating macerals,parameters of Bitumen "A" and ROCK-EVAL supported that they can generate oil and gas.Inerlinite is by no means simply a bad source maceral for generating hydrocarbon,it can also produce some gas and its hydrocarbon-generating potiential is decided by the evolutionary stage of coal and the other macerals associated with it.However,its high porosity may be a good reservoir for hydrocarbon.