A simple polarization-stepping technique in combination with a common-path homodyne interferometer is proposed in order to measure the phase retardation and the fast-axis angle, which are defined as the linear birefringence vector (LBV), of a wave plate (WP). At three different orientation angles of the linear polarization of incident laser beam, two-dimensional (2-D) interference patterns with respect to different orientation angle are recorded by using a CCD camera. Thus, 2-D phase retardation and fast-axis angle distributions of WP are determined simultaneously. In addition, the elliptical polarization and misalignment of the orientation angle of the incident laser beam induced errors on LBV measurement are discussed.