The grinding forces were measured in brittle grinding of glass with three typical shape diamond grits. The influences of grinding parameters and cutting angle of grits on the grinding forces were discussed. The experiment results show that the force signal curves are not symmetric distribution with scratching profile. There are obvious oscillations on the curves of normal force signals. The value and curve shape of grinding forces of the down-grinding are as same as those of the up-grinding. Grinding forces increase with grinding depth, but decrease with the grinding velocity. The grinding forces obviously increase with the cutting angle of grits. With the same cutting velocity, the grinding forces have good linear relationship with plowed surface area. There is a very good linear relationship between the normal forces and tangential forces for different grits.