Design and use of drill bit is an important process and technique and has become a main factor to effect ROP, core and hole quality, and drilling cost. A wealth of experience about designand use of drill bit has been accumulated in the geologic core drilling and foundation construction. An expert system is a computer system built with the method of intelligent base programming, it includes the expert's knowledge and experience about one particular field, uses theknowledge to make nit.elligent policy decision as the expert in this field. We developed the expert system of design and use of drilling bit by utilizing the CM. I tool on G. W. 286 computer.The expert system includes the diamond bit of small diameter and construction bit of largediameter. The expert system of small diameter diamond bit consists of two controlling knowledge bases and five special knowledge bases on the bit design and use of single pipe, doublepipe, wire line coring, rotary and impact and electric plating. The establishment places emphases on matrix composition, system of water way, drilling parameter, balance of drilling.pressure and judge of bit sharpening. The expert system of large diameter engineering construction bit consist of two controlling knowledge bases and five special knowledge bases on the bitdesign and use of roller cone, spiral, scraper and inserted tungsten. The establishment puts emphases on construction, appearance, using condition and measure according to the formationand drill pattern.