The die-board and PMMA reflectivity of CO2 laser were measured by the calorimetric method for the explanation how the kerf shape of laser cutting higher absorptive nonmetallic materials formed．The results indicate：1)that the reflectivity of perpendicular polarized beam will increase with the growth of the incident angle；2)that with the incident angle below 60 degrees the reflectivity of parallel polarized beam is small and it will diminish gradually with the growth of the incident angle while with the incident angle above 60 degrees the reflectivity will increase abruptly with further growth．The calculation results aye in accordance with the theoretical results．