The integral dropper of a catenary system of Beijing—Tianjin high-speed railway was taken as the research object, and a coupling model of the pantograph-catenary system was established using a finite element method. The integral dropper was equivalent to a nonlinear spring which can only bear tension, and the coupling of the pantograph-catenary system was realized by a penalty function method. After verified the simulation model, the transient dynamic performance of integral dropper was studied. Results show that: while the relative speed between pantograph and catenary is 300 km/h or 350 km/h, the dominant frequency of dynamic force of different integral dropper in the same span is the same, and the dominant frequency is 7.8 Hz; While the relative speed is 300 km/h, the transverse vibration amplitude of different dropper′s upper and lower node is very small, which is less than 3 mm. Both the upper node and the lower node in a same dropper have the same vertical vibration phase, and the vibration dominant frequency of different dropper′s upper node or lower node is 1.42 Hz; while the relative speed range from 250-350 km/h, 3# dropper has a longest relaxation time compared with other droppers in a same spin.