A set of measuring device for the transmittance of the solar attenuation screen is introduced. Two set of data are required: light signals transmitted through the test fixture with and without the solar attenuation screen. Then the solar attenuation screen transmittance is the ratio of the screen-on data to the screen-off data under the same geometric condition. The method of polynomial fitting interpolation is proposed, which is used to solve the problem of dense on-orbit angle. The error of the method is less than 0.04%. The results show that the average transmittance of the solar attenuation screen is 13.3%, and the uncertainty of the device is better than 0.54% (covering factor k=2). The results indicate that the device can provide data support for the use of the solar attenuation screen on orbit.