The invention provides a thread loosening control system of an industrial sewing machine. The thread looseness control system comprises a thread loosening mechanism arranged inside an industrial sewing machine body and used for controlling action time and thread loosening degree of the thread loosening mechanism. The thread loosening control system comprises a thread loosening drive device, a thread tension sensor, a position and rotational speed detection unit, a moment of force detection unit and a control unit. The action time of the thread loosening mechanism can be controlled through feedback signals of the tension sensor and the position and rotational speed detection unit by adopting speed closed-loop control, and closed-loop control over the moment of force of the thread loosening mechanism is achieved by detecting signals of the moment of force of a thread loosening motor; accordingly, the problem that in the sewing process, control over the action time and thread loosening strength of the thread loosening mechanism is inaccurate is solved, the rejection rate of sewn products is lowered, production efficiency is improved, and advancement of a digital control system of the industrial sewing machine is improved.