This paper presents a simplified approach to analyze the dynamic response of offshore jacket platform based on Timoshenko beam theory. In the study, the jacket platform is simulated as a non-uniform cantilever beam structure subjects to random waves. The assessment of dynamic performance is based on the power spectral densities, variances and spectral moments due to wave spectrum. A combination of Pseudo- excitation and Ritz method is proposed and adopted, such as the dynamic characteristics of the jacket platform can be solved more efficiently without a need to examine the modes of vibration. The proposed analytical method also provides a more straightforward solution to determine the dynamic response of offshore jacket platforms that meet the required level of engineering practice for preliminary design.