Abstract: An adaptive algorithm for generating smooth motion profile is proposed by using piecewise 3-order spline curve. The algorithm provides second derivative of displacement，first derivative of speed and continuity of acceleration with speed，acceleration and jerk constraints，which avoids the occurrence of intense vibration in high-speed machining. The influence of these constraints on the motion profile is analyzed. Based on these constraints，the algorithm can automatically adjust the period of each transition procedure in order to obtain smooth motion profile. The strategy of piecewise constant speed and smooth motion control is also introduced. The algorithm is effective and has been adopted by CNC system of newly deve-loped high-speed glass engraving machine center.

Key words: 3-order spline curve, CNC system, High speed machining, Piecewise constant speed, Smooth motion profile