In order to effectively manage overload and provide data support for road design and planning, a dynamic weighing system for expressway based on PVDF sensor is proposed. Aiming at PVDF sensor signal, charge amplifier circuit, SCM signal acquisition circuit and SD card storage circuit are designed. The sliding average filtering algorithm is proposed to further process the sampling signal, and the design process of the software system is analyzed. In order to verify the accuracy of the data processing scheme, outdoor site simulation tests were carried out. Furthermore, the data of vehicle load spectrum are obtained by field test, and the structure of the actual traffic volume is obtained by analyzing the data. The test results show that the weighing system can meet the accuracy requirement of dynamic weighing and has high practical application value.