The invention discloses a seismic oscillation input method for a steel gate of a high dam body. The method comprises the following steps: determining a gate seismic oscillation input mode; establishing a relational expression of acting force applied to the gate by the dam under the action of seismic power; collecting data required in the relational expression of the acting force applied to the gate by the dam under the action of the seismic power of the corresponding part; establishing a before-gate seismic hydrodynamic pressure relational expression; determining seismic oscillation input dataof the three connection modes; and constructing a comprehensive finite element model of the gate and water seal boundary combination, establishing a gate structural mechanics equation, and performingdam body steel gate seismic response analysis. The dam body steel gate seismic oscillation input method effectively solves the problem of gate seismic analysis on the basis of not carrying out high dam and gate multi-component coupling seismic analysis.