In this paper, the structure and operation principle of BLDC motors are introduced, a simple mathematical model is figured, a speed PI controller was designed, a simulation model to control 3-phase BLDC motor speed in Matlab/Simulink was built, an analytical study of the Speed, Current, Electrical Torque, Back-Emf waveforms, during no load was done, the effect of adding external load in different load torque values are studied. The effect of adding external load torque during operation is studied also.