As a classical instrument for measuring the infrared radiation intensity of the aero-engine,the infrared spectral radiometer has the advantages of high spectral resolution,high measurement precision,fast response,wide spectral range and so on.However,the infrared spectral radiometer needs to select an appropriate lens according to the size of the measured target and the measuring distance.The infrared radiation intensity of the aero-engine can be obtained by multiplying the measured spectral radiance by the effective field-of-view area of the lens.Due to the processing and assembly errors of the manufacturer,the field-of-view angle of the lens of the infrared spectral radiometer will be deviated from its default value,leading to testing deviation.In order to measure the field-of-view angle of the lens of the infrared spectral radiometer,an effective method is designed and a measurement device is made,which is used for measuring the effective field-of-view angle of the standard lens of the VSR-3 infrared spectral radiometer.The measurement results show that the effective field-of-view angle of the lens presents a 4% deviation from the factory default value.Through deviation correction,the precision of infrared radiation intensity measurement of the aero-engine can be improved.