Abstract: Aiming at the problem that transmittance parameters of infrared optical system cannot be accurately measured, the measurement and calibration technology for spectral transmittance of infrared optical system were studied. Based on the analysis of measurement methods such as integrating sphere method and large-area uniform source method, a calibration device for spectral transmittance of infrared optical system based on method of reflection was studied and constructed, and the complete quantity traceability and quantity transmission chain of spectral transmittance were established. The device was used to measure the spectral transmittance in the wavelength range of 2 µm~14 µm, and the uncertainty analysis of the measurement results showed that the result was 2%. Compared with the previous measurement device, the measurement results of the proposed device have higher accuracy and reliability.