Abstract: Previous bit wear monitoring methods which based on theory of MSE analyzed the normal trend line of MSE,which is qualitative analysis method.There was not a quantitative calculation method for bit wear.This paper chooses a reasonable torque calculation model to optimize the MSE calculation model and chooses appropriate ROP equation of PDC and cone bits which consider bit design parameter,cutting structure,drilling parameters and bit wear fully.This paper proposes a new method that combines the qualitative analysis and considering such factors as ROP,WOB,RPM,torque and bit design parameters etc,the new approach uses ROP models and some logging data to calculate MSE,Cs and bit wear grade factor.It has been applied in several bits wear monitoring,such as Well B in Junggar Basin,Well A in South China Sea Basin and Well C in Tuha Basin.Compared with measured data,the relative error of accuracy of calculated results of PDC bits is 9.87%,and that of cone bits is 21.15%,therefore,this new method has great accuracy and is more suitable for PDC bits.