An identification algorithm for instantaneous engaged cutting edge elements in five-axis milling is presented in this paper. An application of curve and surface intersection is used for filtering the engaged cutting edge elements roughly on any cutter location (CL) point at any machining time. And then the real engaged cutting edge elements can be further selected with computing entrance angle and exit angle of every axial disk element. Based on envelop theory, the swept feature-line can be calculated. According to the swept feature-line, entrance angle and exit angle of every axial disk element can be obtained in the cutter coordinate system. The validity of the algorithm mentioned above is verified by examples with various cutting depths.