Abstract: The benefit exponential model of bit was set up by analyzing a great number of working information of bit. The application effect of bit can be evaluated by the model according to the aggregate indexes of three factors such as the footage of bit, penetration rate and bit cost. It showed that this new method had no difference with the evaluation method of bit cost per meter overall. But the new one showed the henefit fully. Using the model, the bits in the formation of Bohai oilfield can be evaluated. 16 kinds of bit were optimized. After the on-site application, good economic benefit were obtained.