The alarm system in controlling the automobile speed is presented, without change of the original structure, and the design scheme of the system implements sampling, measurement, computing, real-time alarm and delay-time control for the automobile speed according to the safety of the automobile driving. Then, the speed is randomly stored so as to insure the correct data and to effectively analyze the data. Especially, the key techniques of the speed measurement and the refresh storage are pesented in datail in the system.