Overall response induced by unbalanced traffic load is one of the key issues for multi-pylon suspension bridge (Virlogeux,2001).The current traffic load model for bridge design in china is referenced from other country codes in some extent,but is not suitable for long span bridge design as its loading pattern and load value present small probabilities in actual conditions (Ruan and Zhou et al,2013),especially for multi-pylon suspension bridge.Thus it is of great importance to study the load responses under actual traffic running conditions.