Methods such as field investigation and statistical analysis were used to analyze the characteristics of auxiliary through lane (ATL) at signalized intersection. Variation of traffic volume, headway of vehicles, lane utilization ratio and types of accidents were chosen as the characterization parameters and the traffic operation characteristics of ATLs were analyzed. Results show that the ATL plays an important role in enhancing the operational capacity of signalized intersection, but the headway of vehicles driving on ATLs has obvious characteristics of "two stages", low lane utilization rate and more scratch accidents. Means like traffic sign layout improvement measures, transition section, sight distance and downstream length should be applied to improve traffic operation conditions of ATL.