Abstract: In order to avoid self locking and to reduce frictional force in cam's motion, the pressure angle of canister cams' curve must be restricted, so that the micro servo motor's torque can be the smallest. Simulation design and analysis for the auto zoom lens of a digital camera is introduced. The assembly structure drawing of a canister style zoom lens with 3 times optical zoom is simulated, and the pressure angle expression of the canister cam analyzed. The optical design and structural design, analysis of the zoom lens, process of focus change in the zoom lens and technical requests to the parts of the zoom lens are discussed too.