Abstract: In order to grade the used bits, IADC published the Three Point Dull Bit Grading Scheme. Because it cannot fully evaluate the dull bit characteristics, IADC published the Eight Point Dull Bit Grading Scheme to replace the old scheme. In comparison to the old scheme, the new scheme can fully evaluate the tooth/cutter wear, dull features and the reason pulling of the used bit. It's convenient to users who refer to the dull bit grading features to select bits and choose reasonable drilling parameters in the offset wells. So it's suggested that the drilling personnel are better to use the Eight Point Dull Bit Grading Scheme to evaluate the used bits rather than the Three Point Dull Bit Grading Scheme.