High precision polarization-scanner (POSP) can obtain high precision multispectral polarization-radiation information of the target by using the simultaneous polarization-measurement technology of partial aperture and partial amplitude. Its measurement accuracy is one of the key indexes affecting in-orbit application of load. After the instrument is developed, polarization and radiometric calibration and measurement accuracy evaluation are completed under laboratory conditions. To test laboratory calibration results, we carry out the natural target detection under the ground of the verification experiment. The sky is scanned along the main plane of the sun with POSP in a clear day. The data of sky radiance and polarization degree obtained are compared with the data collected by CE318N sun-sky polarization radiometer at the same time, and the factors affecting the data of the two instruments are discussed. The experimental results show that the two instruments have a good consistency, with the consistency deviation of radiance and polarization less than 4% and 0.005, respectively. The accuracy of POSP laboratory calibration and the detection ability under natural targets are verified, which can provide a basis for the subsequent processing and application of space-borne data.