Inertial Navigation System can hardly be used because of its high cost and low accuracy. A new type of autonomous inertial navigation system is designed. It uses DSP as the navigational calculating and controlling processor. The arithmetic of navigational calculating is based on quaternion algorithm so as to determine the object's speed, position and posture. The result indicates that relatively numerical deviation is 10-4%, relatively test deviation is 10-3% and calculation time is 40μs. The weight, cost, volume is reduced in this design. It has wide market application prospect.