By using matrix optics method, expressions of two types of optical parallelism in pentaprism were obtained. An relationship between optical parallelism and normal vector of working surface was analysed. An experiment device based on Agilent laser interferometer and DHC 3D rotation platform was established. With angular measurement function provided by the device, optical parallelism of a pentaprism made by Thorlabs were measured. The experimental results are consisten with the calculation of analytical expressions, whose deviation is no more than 4%. Conclusion indicates that changes of roll angle and yaw angle in practical application are equivalent to alteration of optical parallelism. It means that the jitter errors of online measurement and fabrication errors can be in-situ calibrated simultaneously by coordinates transformation. The study is useful for manufacturing, adjusting and pre-calibrating a pentaprism in optical system, and the conclusions above can be a good help in high-precision optical surface profiler metrology in practice.