Objective To study the distribution characteristics of sunlight spectral power. Methods Sunlight spectral irradiation curves within the range of 200 nm-800 nm in the plateau, northwest desert and tropic areas were measured. The distribution characteristics of sunlight spectral power in different areas, weather conditions and scanning speeds were analyzed respectively. Results The irradiance strength within the UV and VIS wavelength coverage in the plateau area was higher than in the northwest desert and tropic areas. The total irradiance within the range of 200 nm- 800 nm on cloudy days was 1/4 lower than that on sunny days, while the irradiance within the range of 200 nm-400 nm on cloudy days was only 54% of that on sunny days. The effect of the scanning speed of spectrometer on the determination results was neglectable. Conclusion The cut-off point of sunlight wavelength, the spectral irradiation at 340 nm wavelength and the irradiance within different wavelength coverages could be used as reference for light source selection and spectral power control in laboratory exposure tests.