Based on carbon and hydrogen isotopic compositions of gaseous alkanes in the Tarim Basin, two type gases were recognized: oiltype and coaltype. The former with lighter carbon (δ13C2＜-28‰,δ13C3＜-25‰) and heavier hydrogen was mainly derived from the marine sources in Cambrian-Lower Ordovician or Middle-Lower Ordovician, distributing mainly in the platform of the basin; the latter with more negative δ13C δ13C2＞-28‰,δ13C3＞-25‰) and less negative δD originated from continental humic in TriassicJurassic, distributing in the foreland of the basin. The partial reversal trend of carbon isotopes for gaseous alkanes in the Tarim Basin may be related to thermal maturity degrees of sources. TSR is also a reason for the partial reversal trend of carbon isotopes in some regions. The relatively higher 3He/4He ratio of the natural gas from the Tarim Basin may be caused through the mixing of a little deep gas remained in rocks into the gas reservoirs.