In high power fiber lasers,the mechanical stress on optical fiber will lead to deterioration of laser beam quality and temperature rising of optical fiber.To solve the problem,the influence of optical fiber deformation on the mode distribution of signal light is analyzed theoretically.The heating model of fiber is established.The effects of stress on optical fiber heating and laser beam quality are studied by experiment.The results show that stress induced optical fiber deformation will cause directional changes in beam quality.The M2 value decreases slightly in the direction of force and becomes larger in the vertical direction.When output is 100 W,the maximum change of M2 value caused by stress is 0.39 and the maximum temperature rise caused by stress is 12 ℃.The temperature rise of the CPS using silastic is controlled within 5 ℃ and the M2 value caused by stress is controlled within 0.05.