Abstract: In order to measure thermal effect parameters of high-energy laser material on-line, a testing device with aperture of 50mm was specially designed. Collimating He-Ne laser was used as light source. The optical-path difference of testing beam after passing the material was measured by Hartmann-Shack wavefront sensor. According to wavefront aberration decomposition theory and wavefront transformation relationship, thermal effect parameters of high-energy laser material were gotten. Measurement uncertainty of the device was analyzed and evaluated. The system parameters which affected measurement uncertainty were calibrated. Finally, a comparative experiment of measurement uncertainty was designed and completed. The result shows that, the measurement uncertainty of system wavefront aberration is 0.06λ. The measurement uncertainty is 8.4% with thermal focal length of 30m~120m. The system can be applied to measure thermal effect parameters of high-energy laser material online.