A new method for estimating the wear of disc cutters is proposed to improve the management of shield tunneling operation. Machine torque per unit penetration, called the coefficient of excavation K_T, is a useful parameter for relating the machine performance data and the wear of disc cutters. The invsetigation on data sets obtained from four construction sites shows that the wear rate is proportinal to the squre of K_T regardless the condition of tunneling. On the other hand, the coefficient in the formula depends on the conditions except hardeness of the ground. Thus, wear of disc cutters can be evaluated from the cumulative value of K_T². Outline of the equation and the results of the investigation are given in this paper. The way of applying this method to the management is also suggested.