The deviation during empty running, if the deviation is weakened or normal after adding the conveying material, is caused by the looseness of the conveyor belt or the excessive initial tension. If the tension is too large, the conveyor belt jumps off the idler roller and floats and swings during operation. If the tension is too small, the friction between the roller and the conveyor belt will decrease, the power of the conveyor belt to advance longitudinally will decrease, and the resistance of lateral movement will decrease, resulting in deviation. Appropriate additions and reductions can be taken to solve the problem. The tensioning stroke can be adjusted for the belt conveyor with screw tension or hydraulic tension.