The transient response analysis of a jacket offshore substation is based on the time domain integration method. The transient response caused by the initial conditions usually contains higher order vibrating components，which requires that the time domain method has to take a sufficiently small calculation time step to get the accurate results. In this paper，a frequency domain calculation method based on Laplace transform is proposed for the transient response analysis of an offshore substation. In this method，the poles and residues of the transfer function are obtained by eigenvalue analysis of the vibration system. Then，the poles and zeros of the transfer function are calculated. Meanwhile，the initial conditions are considered in the pole and residue of the transient response，and the time-domain transient response is obtained by Laplace transformation. The results show that the transient response calculated by the method is in good agreement with that calculated by the Newmark-β method. Besides，the error caused by large time step of the Newmark-β method can be avoided.