In the calibration process of the amplitude-division polarization imaging detector, a nonlinear least squares fitting method was proposed to solve the problem of strong coupling between the error introduced by the calibration system and the super-influencing factors of the detector''s own error. It substituted the main factors affecting the errors of the detector and the calibration system into the fitting equation in the form of unknown parameters for calibration calculations. The accuracy of the calibrated detector was verified under an incident light source with a wavelength of 532 nm. The polarization angle error of detecting linearly polarized light is below 0.2°, and the linear polarization error is below 2.5%, the circular polarization error of detecting left-right circularly polarized light is below 3.5%, which satisfies the application of sky polarization detection. It can be seen that the nonlinear least squares fitting method can effectively calibrate the amplitude-division polarization imaging detector.