By using C sharp tool to design the automatic calculation system of navigation astronomical orientation, base on altitude difference principle, and arithmetic models of aster true altitude, aster Greenwich hour angle, aster declination and ship position, were arranyed. After the practical application and software testing, in comparison with the hand-worked calculation, it concluded that this system enables the rapid calculation and reliable results, thus meeting the needs of navigation and avoiding the errors or mistakes that causing by hand-worked calculation. Thus the results prove its the practicability and reliability.