Abstract: The entangled photon pair in quantum communication experiments is produced by laser pumping nonlinear crystal. In the experiments, it is necessary to adjust the optical axe of uniaxial crystal to the vertical plane. Usually, the optical axe direction is determined by polarizer, but this method can only give the two engine directions of the crystal. The relation between the direction of the optical axe and the trend of the interference fringes was analyzed. The experimental method and results for calibrating the optical axe direction of uniaxial crystal are offered. The experiment results show that the optical axe direction is perpendicular to the trend of interference fringes.