在随钻过程中，在线识别地层岩性一直就是地质人员和钻井工程技术人员十分关心的问题．使用ＰＤＣ钻头钻井时，岩屑破碎很细，通过岩屑录井来判断地层岩性十分困难．针对ＰＤＣ钻头的切削机理，本文从ＰＤＣ钻头切削刃受力平衡角度出发，建立了ＰＤＣ钻头钻井时地层岩性随钻评估模型．现场初步试验表明，本文所给出的模型具有一定的合理性和实用性． During the drilling process, on-line identification of formation lithology has always been a concern for geologists and drilling engineers. When drilling with a PDC bit, the cuttings are very fragile, and it is very difficult to judge the lithology of the formation by cuttings logging. Aiming at the cutting mechanism of PDC bit, this paper sets up a lithologic evaluation model while drilling PDC bit from the point of force balance of PDC bit cutting edge. Preliminary tests on site show that the model given in this paper has some rationality and practicability.