Abstract: Automobile users with elastic demand may be most affected by congestion pricing in all traveler groups ."Relative congestion fee"is introduced as a policy variable to represent the influence of congestion pricing on the mode choice .A mode choice model with a nested structure is developed for considering the influence of congestion pricing to dif-ferent traveler groups .An RP survey and an SP survey to the automobile users with elastic demand from Nanjing's Xin-jiekou Commercial District are implemented and the model parameters are estimated using such data .The results show that the females ,low-income group ,IC card holders ,and travelers traveling with short-distance and high-frequency are more likely to switch from automobile to public transit when faced with the congestion pricing policy .Finally ,the elastic-ity to travel time and the charges of congestion pricing are analyzed for travelers under different congestion levels .It is found out that (1)the elasticity to travel time reveals the overall service level of the trip mode ;(2) the critical value of travelers'"significant"sensitivity to congestion fee is 13 .25 .