In order to study the intrinsic relationship between the polarization flipping effect and the phase retardation based on laser feedback, the output intensity and polarization state of the laser were observed during the tuning of the feedback cavity length by using a microchip Nd∶YAG laser (central wavelength of 1064 nm) as the light source and two relative rotating λ/4 wave-plates in the feedback cavity to change the phase retardation. The results indicate that, with the increase of phase retardation in the feedback cavity, the indentation depth of the polarization flipping position gradually deepens, and the width of the light intensity modulation waveform of the two polarization states tends to be the same. When the phase retardation in the feedback cavity is 90°, the duration of two orthogonal polarization states to be the same in an intensity modulation period, and each polarization flipping corresponds to a change of λ/4 feedback cavity length. The variation of the characteristic point of polarization flipping caused by different phase retardation provides a potential measuring method for phase retardation of waveplate at 1064 nm wavelength. Meanwhile, the change of phase retardation shapes the output light intensity waveform of laser, which provides a basis for optical subdivision of laser feedback fringe (self-mixing interference fringe).