Abstract: Stochastic dynamic response analysis of fixed offshore platforms to nonlinear random wave forces is represented systematically. Effects of fluid-structure interactions are considered. The main problems which should be solved are linearization of nonlinear drag forces and diagonalization of coupled general damping matrices. Statistic equivalent linearization technique is therefor used together with an iterative proeedure. The simutaneous nonlinear stochastic differential equations are finally transformed into several independent linearized ones and are then solved readily. SELIM and SELIM-1 computer programs are developed accordingly. The calculation results are satisfactory. For an offshore tower with seven degrees of freedom, the iterative errors become less than five persent after two or three cycles of iteration.