For the problem of trajectory tracking of a time varying constrained harmonic drive based modular and econfigurable robot(MRR), a decentralized integral sliding mode control method based on the joint torque feedback echnique is proposed. In the condition of existing coupling model uncertainty, a high-performance control can be achieved ithout using the force/torque sensor. Based on a harmonic drive model, the joint torque is estimated by using only position easurements of each MRR module, and the subsystem dynamic model of MRR is formulated. Based on the variable gain uper twisting algorithm(VGSTA), a decentralized integral sliding mode controller is designed to compensate the model ncertainty and reduce the chattering effect. The asymptotic stability of the system is proved by using the Lyapunov theory. Smulation results show the advantage of the proposed controller.