During the electromagnetic launchers, the Brushless DC linear motor works on the accelerated state, the range of velocity is wide, so the research on the influence of the speed upon the commutation force ripple is very important. The paper establishes the mathematical model of BLCDLM on the consideration of all factors that affects the commutation force ripple. Common formulas of the current, commutation time and force are derived by solving the mathematical model, and the curve of the current is given. Influence of speed and the back-EMF on the force ripple is analyzed in detail. At last, the results of simulation validate the analysis of theory.