The invention relates to a servo control based actively follow-up let-off compensation device which comprises a rack, a supporting shaft, an electric drive pusher and a tension roller servo motor. The tension roller servo motor is connected with the electric drive pusher, the electric drive pusher is connected with one end of a connecting rod a and is used for driving the same to move vertically, the other end of the connecting rod a is fixedly connected with the supporting shaft, the supporting shaft penetrates the rack to be mounted on the rack, and the supporting shaft penetrates one end of the rack to be connected with a tension roller through a connecting rod b. The control method includes: setting control parameters of a heald frame servo driver and the let-off compensation tension roller; respectively setting values of command pulse frequency doubling molecule and denominator parameters of a let-off compensation tension roller servo driver and the heald frame servo driver; setting direction of rotation of a heald frame servo motor and the tension roller servo motor; performing electrical signal connection. By the arrangement, digitalized actively follow-up compensation of warp yarn path change scale caused by motion of a heald frame is realized, mechanical compensation is turned into digitalized compensation, and intelligentized control level of a weaving machine is improved.