The invention discloses a flexible driving unit for a robot joint driven by a pulley block and wire rope traction and relates to a flexible driving unit for a robot joint. The invention aims to solve the problem that the conventional flexible driving device for the robot joint cannot realize flexible drive and bidirectional transmission simultaneously. One end of a first pulley traction wire ropeis fixedly connected to an output shaft sleeve; the first pulley traction wire rope is wound with a side fixed pulley guide wheel, a movable pulley guide wheel in a movable pulley device for speed reduction, two bottom fixed pulley guide wheels positioned in the same group, and another movable pulley guide wheel in the movable pulley device for speed reduction in turn; the other end of the first pulley traction wire rope is fixedly connected to a bottom wire rope locker; a second pulley traction wire rope has the same winding mode as the first pulley traction wire rope; and a primary locker and a secondary locker are abutted. The flexible driving unit is used for the drive of the robot joint, realizes the function in a unit form, has the capacity of bidirectional rotating and transmitting, and can replace the work of two artificial muscles.