In a laser heterodyne interferometer, nonpolarizing beam splitters (NPBS) are also the important nonlinear error sources besides laser sources, polarizing beam splitters (PBS), wave plates and other polarizing components. The influence of depolarization effect and misorientation of a multi-layer dielectric NPBS on the nonlinear error is investigated. The depolarization effect is characterized as the reflectance, transmittance, reflection-induced-retardance (RIR) and transmission-induced-retardance (TIR) between the p- and s- components. The producing mechanism of the nonlinear error is accordingly analyzed. Only the RIR and TIR have contribution to the nonlinear error while the incident light is in ideal polarization state. Otherwise the variation of the misorientation and the depolarization effect will introduce nonlinear error, and the error slopes are affected by the elliptical polarization and non-orthogonality. Therefore the error introduced by the same NPBS varies with laser sources used in interferometers. Generally it will be up to several nanometers. A NPBS with steady performance should be selected to seek nanometer even sub-nanometer accuracy. The parameters match between the depolarization effect of NPBS and the polarization state of laser source should also be attached more importantly.