To achieve the sealing requirement, the laser transmission inner channel will add the window with an inclined angle at the end of thin channel, but the temperature rise caused by reflected stray light of the window irradiating the pipe wall will also increase the gas thermal effects. Aiming at the problem of irradiating and heating the straight pipe by the reflected stray light of the sealing window, a coupling simulation model of structure field-gas density field-optical field in the straight pipe was established, analyzing the influence of materials, wall thickness and structural forms on wave front distortion of beam. The analysis results indicate that among three materials of equal quality, aluminum, copper and steel, the beam wave front distortion caused by the aluminum pipe is the smallest, which is only 50% of that of steel and copper; reducing the wall temperature and the beam distortion by adding heat dissipation fins or high thermal conductivity carbon film outside the pipe is not ideal and the wave front RMS value is reduced by no more than 3%; increasing the wall thickness and raising the pipe heat sink are the most effective solutions to reduce the beam distortion, the RMS value of the aluminum pipe outlet reduces from 36.1 nm to 21.4 nm and each order aberration is improved while the wall thickness increasing from 8 mm to 16 mm. The research results can provide a certain reference for the pipe design of inner channel and thermal effects evaluation.