Generally complex 3D contours are divided into a lot of continuous small line blocks by CAD/CAM software. When these small line blocks are used in conventional way, machine tool has to stop at the end of one move before continuing on to the next to meet accuracy requirement, which results in inefficiency. Look-ahead is an intelligent function that aims at adjusting the feed rate automatically to achieve maximum productivity while maintaining accuracy. By now most researchers just utilize the simplest linear acceleration (ACC) and deceleration (DEC) to deal with look-ahead intelligence. A generalized ACC/DEC approach and corresponding optimal look-ahead algorithm based on dynamic back tracking along a doubly linked list are proposed. An improved rounding strategy for reducing interpolation errors is also presented. By using the proposed techniques, arbitrary velocity profiles that offer look-ahead feature and have the desired ACC/DEC characteristics for movement of a lot of continuous line blocks can be generated efficiently. Both simulations and experiments showed the productivity was dramatically increased without sacrifice of accuracy.