Abstract: Based on drilling of Carboniferous-Lower Permian and comparison of the organic geochemical characteristics of outcrop limestone and mudstone in Turpan-Hami Basin, this paper elaborates the influence of weathering effects on organic characteristics of source rock. The analysis indicates that organic abundance of mudstone is generally higher than that of limestone. So far as hydrocarbon source rock is concerned, mudstone is better than limestone thanks to the different sedimentary environment and material sources. The conserving conditions for samples of fi eld outcrops are apparently poorer than those samples of source rock in the deep layers of the basin. If the samples from the same strata and the same lithology become different, at the drilling and outcropping, this phenomenon is related to weathering effects. Weathering effects can exert infl uence on total components of dissoluble organic matters and hydrocarbon content of middle and lower molecules, causing more serious damage on dissoluble organic matters than solid dissoluble organic matters. As compared to limestone, mudstone can more strongly resist weathering effects.