A development of the system software for a small class ship autopilot is presented. A dynamics modeling for small class ship is firstly described. A control system with several operating conditions for the autopilot system is constructed. This is based on the conventional PID control technique. The system is composed of power amplifier, gear unit, and ship dynamics. The ship dynamics is realized by microprocessor. A system software is built up using 80C196KC microprocessor on an one chip format. The autopilot system proposed is simpler to operate comparing to others due to the simple design of the operating panel and economical due to the design of the one chip microprocessor. This also has varieties of expansion to a large scale system because of using high level microprocessor. The experimental results by using a model plant for the autopilot system as well as computor simulation results are given to illustrate the useful ability of the proposed system.