In order to predict online the subsurface damage depth of the specimen induced in grinding of hard-brittle material, a theoretical relationship between the cutting force of the diamond tool and the subsurface crack depth of the specimen was established. This relationship was based on the statistical analysis of abrasive height using probability and statistics. First, based on the indentation fracture mechanics of the hard-brittle materials, the intrinsic association between the propagation depth of the median crack and the indentation depth of a single abrasive was investigated. Subsequently, the number of actual abrasives located on the boundary of the tool end-face was calculated using mathematical statistics, and the internal correlation between the cutting force of the tool and the cutting depth of each single abrasive was developed. Finally, a method for quick online prediction of the subsurface damage depth was proposed (SSDmax=1284×SSDmaxtheo-3623), and its accuracy was verified by an actual grinding experiment of BK7 glass. The experimental results illustrate that this technique can achieve accurate online prediction of the depth of subsurface damage involved in the grinding process.