Abstract: When the machining tool moves along the current path,the points on the cutter blade, whose distance to the free-form surface meets the machining precision,can form a transient path.Based on this transient path,the next tool path can be obtained.This method eliminates the approximate errors of the feed-way and local geometry information.As a result,the precision of too-l path planning is improved.A study case shows that this approach is effective.