The cutting vibration is a very harmful phenomenon, which destroys the surface finish and dimensional integrity of workpieces and quickens the wear of cutting tool. The cutting vibration can be suppressed or reduced by applying the variable spindle speed cutting. In order to investigate the effect of variable spindle speed parameters and cutting conditions on suppressing the vibration, the deeper slot milling tests have been conducted. The results have shown that the vibration occurring in deeper slot milling can be reduced by applying the method of variable spindle speed milling, as long as the variable speed parameters are elected suitably. The values of speed variation amplitude Δn/n0 and speed variation frequency fn of spindle speed trajectory parameter have a great effect on antivibration. Under this article test condition, the amplitude Δn/n0 of variable spindle speed is 20% and frequency fn of variable spindle speed is 0.3Hz.