In this paper, a web-based computational system for ship's hydrodynamic performance and stability is developed. A robust stand-alone program is adopted as the computing kernel in this system. The web-based user interface and the control center are written using Java language. Different to stand-alone programs, this system is able to perform multi-job submitted by different users at the same time. The results can be shown on web browser in tabular and figured forms. Using this system, users can accomplish their job through Internet on any PC. So there is significant improvement on convenience to undertake such a calculation task. After the system is constructed, two cases, including calculations of hydrostatic performance of a submarine, and haulage planning of heavy mechanical equipments. are carried out using the system in this paper.