The effect of wave plate on nonlinearity of single-frequency polarized laser interferometer in nano measurement is researched. An error analysis model of multi-wave-plate is established based on Jones matrices theory. The nonlinear error in interferometer induced by λ/2 and λ/4 wave plates is analyzed and nonlinear error caused by the position of wave plate is experimentally studied. The results indicate that the adjustment accuracy of wave plate position has a great influence on measurement. In the range from 0 to 5°, the non-linearities caused by λ/2 and λ/4 wave plates are 6.5 nm and 9.5 nm respectively. The research results provide a beneficial reference for optical path adjusting and nonlinear errors compensation of orthogonal polarized laser interferometer.