A numerical study of a scaled real model is carried out in time domain to investigate the dynamic characteristics of an existing jacket offshore structure located in the red sea in Egypt. The hydrodynamic force includes wind, wave, and current effects on the structure. A parametric study is considered for multiple wave parameters (wave height, wave period and wave direction). Airy's linear wave theory is used, the results include displacement, velocity and acceleration in time domain with the different wave parameter. In this study, a numerical study were carried out for a two modified models (I, II) for the existing (in operation) fixed jacket type platform. The main objective of the study is to compare the dynamic response of the two modified models with the existing one under regular and random waves. Improvement of responses were observed as will be shown in the results.