A constant scallop-height tool path generation algorithm for triangular mesh surface based on the tool envelope surface is proposed. The algorithm firstly deduces the equation of tool envelope surface, and then the scallop curve can be obtained by the interaction calculation of the two neighboring envelope surfaces. Therefore, the accurate scallop-height can be calculated in the two steps of global searching and local searching. According to the result and the judgment criterion of the constant scallop-height tool path, the optimal CL point can be obtained. Finally, interference detection and processing is carried out for the current CL point. Experiment results indicate that the proposed algorithm is feasible. It can obtain constant scallop-height and shorter tool path without interference, and it can improve the quality and efficiency of machining.