The integrated design and laboratory calibration method of a multi-band polarization imager were presented. The polarization calibration accuracy was validated by a polarized light source whose degrees of polarization (DOP) is adjustable. The results showed that the relative DOP errors of 490 nm and 670 nm band are less than 1.6% and 1.7%, respectively, when the DOP of the polarized light source is less than 0.6. The software system of the multi-band polarization imager was designed as well, and the function modules and automatic observation algorithm of the software were described in detail. Finally, the field operation stability of the instrument as well as the function and practicability of software design were verified by its field depolyment in Dunhuang radiation calibration site, Gansu, China.