Vehicle load is critical for safety assessment of bridge structures in operational condition. This study focuses on modeling vehicle load based on long-term weigh-in-motion (WIM) data from a long-span cable-stayed bridge. Two key issues in the modeling, i.e., vehicle selection and transformation of data statistics to a deterministic load model, are addressed. In the established model, the concentrated load is found to be much greater than the value used in the design stage. The result suggests the importance of vehicle load model from WIM data and it should be used for safety assessment of operational bridges.