The dynamic weighing technology is multi-domain comprehensive technology, including the mechanics of materials, dynamics, the technology of sensor, the technology of electronic information and so on. Vehicle weigh-in-motion system is a detection system which is used to measure the weight of the moving vehicle. With the development of the transport industry output and commercial trade, Vehicle weigh-in-motion technology is playing a more and more important role. At the same time, the accuracy of the weigh-in-motion data has become the centre of attention. In this paper, use the method of least square and polynomial fitting and the MATLAB mathematical software, by studying and analyzing a mass of weigh-in-motion data，the fitting curve of the vehicle weigh in different speeds is obtained. According the variation law of fitting curve, further improvement need to do in certain standard and weigh carefully as to the true quality when the vehicle is in some speed region.