The main error sources for measuring phase retardation of Wave Plate (WP) based on laser frequency splitting technology are analyzed. And the systematic errors, caused by the initial phase retardation of laser and misalignment of WP, are compensated. Error analysis shows that as to multi-order WP, the measuring uncertainty is 1.7′ and as to zero-order WP, 0.8′. Its measurement performances are tested in experiments, including comparing the measurement results when WP is aligned or inclined to the laser axis, measuring the phase retardation at different points among the WP aperture;and evaluating the misalignment angle between WP optical axis and its surface. According to experimental results, this system demonstrates the repeatability and reproducibility better than 0.02°, and the uncertainty better than 2′, viz. about λ/10⁴.