The clastic reservoir of Carboniferous Karashayi Formation has become important substitution to the Ordovician carbonate reservoir in the Tahe Oilfield. The Karashayi sand and mud thin interbedded reservoir is heterogeneous and laterally variable. On the basis of analyzing the features of the curves, the authors built a lithologic index curve based on the integrated gamma ray curve and neutron porosity curve. The characteristic curve was used to invert the reservoir. A comparison with the ordinary acoustic impedance inversion shows that the characteristic curve can improve the inversion effect remarkably and recognize the thin interbedded reservoir efficiently. The new method was used to identify thin beds in the Tahe Oilfield, with satisfactory results obtained. This method has provided a new simple and effective means for the study of Carboniferous clastic reservoirs in the Tahe Oilfield.