On the basic of dynamic model of vehicle-bridge coupled vibration, the influencial parameters on the impact factor of each member in butterfly-shaped arch bridge were studied by the self-compiling computing program, such as velocity of vehicle, distance of eccentric load, structural damping, road roughness, traffic direction, wheelbase, vehicle-to-vehicle distance, vehicle number and structural design parameters. The results show that: (1) as a whole, the impact factors of main cable forces will increase with vehicle velocity; (2) the impact factor of transverse displacement at vault of major arch ribs on eccentric side will increase with the increment of the distance of eccentric load, however, the impact factor of vertical displacement will decrease rapidly; (3) the increment of the structure damping will make impact effect weaken; (4) the impact factor varies along with the grade of road roughness; (5) there is great difference of the impact factors on the symmetric members when the driving direction is different; (6) there is an optimum rise/span ratio that minimizes the impact factor of mid-span deflection; (7) the impact factor will be reduced obviously when the nielsen system is used.