In this paper, a new impedance control method based on pressure distribution for wearable assist robot on multi-joint part is proposed. Generally, assist robots were designed based on assisting for a simple joint body part of the user such as elbow, knee, limb and so on. These robots can be similar structure to the assisted body part, and they can follow the user's movements. On the other hand, it is difficult that the robots have the similar structure to the multi-joint body part of the user such as shoulder, waist, back part and so on. Therefore, the robots assisting for multi-joint body part cannot follow the user's movements and it can cause unforeseen contact state between the user and the robots. There are conventional methods to follow the user's movements on a simple joint body part based on joint torque between the user and the robots, however, they have not been evaluated on the robots for multi-joint body parts. In addition, because torque is resultant force of physical contact force occurred between the user and robot, the direct contact state have not been considered. In this paper, a conventional method based on torque is implemented to the multi-joint robot for assisting back part of the body. Also, a new impedance control based on physical contact forces measured by pressure sensors is proposed. The conventional method and the proposed method are evaluated based on maximum value of contact forces on computer simulations.