The utility model provides a balanced tension device of swing, its mounting panel that has included the vertical setting of support and fixed action, transversely locate the cylinder on the mounting panel, locate the mounting panel rear portion and be in the servo motor below the cylinder in vertical direction, vertically locate right -hand rotatable swing arm of mounting panel, locate the godet roller of lower extreme in the swing arm respectively, the center pin that runs through the swing arm middle part, be fixed in the other pendulum piece that is used for perception swing arm rotation angle of swing arm center pin, locate the angle encoder that the measuring swing arm swing angle mounting panel rear portion and that the swing arm links to each other just links to each other with servo motor and cylinder, the cylinder includes the cylinder and is used for driving the rotatory piston rod of swing arm, the tip and swing arm pin joint in the screw of piston rod, servo motor including the motor main part of locating the mounting panel rear portion, run through and locate its anterior output shaft that is used for installing yarn group behind the mounting panel. This device work efficiency is high, with low costs, tension control is accurate.