The invention discloses a controllable composite sealing device and for tunneling machine main drive sealing and a sealing method. A combination of magnetic sealing and lip-shaped sealing are adopted for the sealing device, active control over the tunneling machine main driving sealing performance can be achieved, tunneling machine main drive sealing can adapt to various work conditions, and the performance of main drive sealing can be effectively improved. The situation that due to the fact that sealing is damaged or an abrasion clearance is too large, main bearing gear oil is leaked or mud particles enter a gear box is avoided, and normal operation of a tunneling machine is guaranteed. According to the method, adjustment and control of sealing are achieved by changing the matter state of magnetorheological fluid filled in a main drive sealing clearance, the sealing clearance can be automatically adjusted according to abrasion conditions, the sealing performance is effectively improved, and adjustment and control of sealing pressure can be achieved.