Abstract: In order to develop a high-precision speedometer so that the mistake and missing punishment of the traffic administration can be avoided, a laser speedometer with a diode laser source was designed based on AT89S52 single-chip microcomputer.Comparing the field test results with the theoretical one, the relative error was 0.1% order of magnitude.It not only supplies a kind of new precise speedometer to measure the instant speed of vehicles on the road,but also supplies a new calibration instrument for radar speedometers and reflex laser velocimeters.