The principle of laser synthetic-wavelength nanomeasurement interferometer is described. The nonlinear errors which affect on this interferometer are analyzed. Theoretical analysis results show that nonlinear errors caused by nonorthogonal polarization, elliptic polarization of laser source, nonideal polarization beam splitter and corner prism are second or higher order polarization error, the comparable experiment of laser synthetic-wavelength nanomeasurement inteferometer and a heterodyne interferometer was performed. The maximal error of laser synthetic-wavelength nanomeasurement inteferometer is 2.1 nm, while the maximal error of heterodyne interferometer is 7.5 nm.