Abstract: Along with the tendency of high speed weaving and diversified varieties of fabric,the let-off mechanism faces new requirements.In order to adapt to weaving,the let-off motion must be controlled accurately.Based on the typical let-off mechanism of available weaving looms,this paper introduces a kind of mathematical model with PI compensating network for warp tension control.It adopts an off-line method of system identification to obtain the transfer function of the let-off model.This method measures tension several times at one turn of loom shaft,uses the average tension value of a repeat of textile weave as looming tension,and introduces tactically a compensation factor to correct any errors of tension on weaving in consideration of the change of beam diameter.And it controls the speed of let-off motor with PID.The computation method derived can satisfy the demand of real time control.