In order to meet the current demand for high-precision calibration of satellite-borne remote sensors, a high-altitude spectral radiance meter has been developed, which can be applied to the radiance method instead of the traditional site calibration method to improve calibration accuracy. The instrument has a spectral range from 400 nm to 2500 nm, and can be mounted on a high-altitude balloon platform to measure the reflected radiance to the ground directly at an altitude from 18 km to 35 km. The optical-mechanical system of the instrument is mainly composed of a front integrated lens barrel, a dispersion module and the optical-mechanical temperature control module. In order to verify the reliability of the high-altitude spectral radiance meter and the accuracy of the measured data, a comparison experiment between this instrument and the SVC spectrometer of Spectra Vista (USA), as well as a high-altitude flight experiment, was carried out in Dachaidan, Qinghai. The experimental results show that there is good consistency in the radiance measured by the two instruments, with a deviation of the two instruments generally within ±1% and a maximum deviation within ±3.5%. In the high-altitude flight experiment, the instrument can keep stable at an altitude of 25 km in the six-hour flighting, and the temperature of each module and detector remains at the setpoint. In the end, the result of high-altitude measurement radiance was obtained. The experimental result has verified the reliability of the entire instrument, indicating that the developed instrument can meet the high-precision calibration requirements of satellite remote sensors and is suitable for the high-altitude high-precision measurement.