Abstract: In this paper, the way and equipment that detects the drafting force of back zone on cotton spinning frame is promoted, on the base of the analysis of draft theory, detected way of drafting force in existence. Using this way, the drafting force of back zone on spinning frame can be detected on-line effectively. By mechanical analysis way, in the course of drafting the mathematical models of drafting force in back zone are educed; the drafting force is detected on cotton spinning frame utilizing detected equipment of drafting force designed by ourselves. Results indicate: this detected equipment can reflect the size and wave circs of drafting force in back zone, provide a new way of on-line detection of drafting force in back zone on cotton spinning frame and choice drafting process parameters in reason.