Based on 2-D laser sensor, an optimized system for dynamically measuring geomet rical parameters of train wheels is proposed in this paper. The calibrat ion of the system is simplified by combining a 1-D laser sensor and a 2-D laser sensor. Accuracy of the 2-D laser sensor reaches 0.2mm and it ensures that most information of the wheel tread surface is acquired. The geometrical parameters including wheel diameter, flange thickness, flange height, tread wear and rim width can be calculated once the information is processed. In order to improve the measurement accuracy of wheel diameter, a new method for spatial circle fitting is proposed. According to the results acquired in the field, the measurement system can satisfy the requirements of dynamically measuring the geometrical parameters of train wheels.