Machining efficiency of complex surface is an important technology in NC engraving machine. For the purpose of increasing the caving velocity of embedded three-axes high speed engraving machine on complex surface, a novel composite speed control method is presented in this paper. An improved arc inserting method is used to increase the turning velocity by reduced junction angle, so that the whole caving velocity gets increased. To prevent the velocity of short axis motor overshooting, according to the natural characteristic of step motor, a look-ahead feedrate planning method is used to restrict the frequency hopping rate by index decelerating to get the short axis motor smooth running. The results indicate that the proposed method can achieve the purpose of increasing the caving velocity while ensuring the time demand of interpolation algorithm. Compared to the traditional speed control method, this method increases the caving efficiency by 12%.