Abstract: According to the development needs of on-line infrared thermometry of metal organic chemical vapor deposition(MOCVD), a three-wavelength infrared thermometry is proposed, which can avoid the calibration of the effective area of detector hole and the modification of reflectivity. The design scheme of the three-wavelength (1 300 nm, 1 150 nm, 940 nm) on-line infrared thermometry probe and the light path are presented. The probe is used in the 5.08 cm(2 inch) silicon (111) substrate growing 10 μm GaN epitaxial wafer in THOMAS SWAN CCS MOCVD system.Result shows that the accuracy is within 1℃ in the range from 950℃ to 1 100℃, referring to the EpiTT infrared thermometry.The repeatability is within 1.0℃ from 700℃ to 1 100℃.The distance tolerance is 2 mm.Moreover, the probe is used in the 5.08 cm silicon (111) substrate growing blue light LED epitaxial wafer with InGaN/GaN MQW structure in homemade MOCVD system. Result shows that the lowest range of the probe is equally 435℃.The measurement noise of n-GaN layer during growing is at 0.75℃. The analysis of the measured results indicate that the method for single layer thin film epitaxial growth has the certain practicability, however, further improvements are needed for the multi-layer complex structure epitaxial growth.