This paper focuses on the analysis of running conditions and machining processes of conical cam with oscillating follower. Common errors were pointed out in the biased distance cutting. By analyzing the motion of oscillating tapered roller follower of conical cam, a new “3-D curve expansion” model of conical cam was presented trough-outline. Based on this model, a machining method for trochoidal milling was proposed with non-equalization diameter cutter. This new method is a creative and effective way for non-equalization diameter machining for conical cam with oscillating tapered roller follower.