Conceptual discussion on highly nonlinear Duffing type equation of surge motion of TLP gives a deep view on structural response under environmental loads with some simplifications. Such analytical response is a simple form that clarifies important points in behavior of the structure. This paper presents the dynamic motion responses of a TLP in regular sea waves obtained by applying three methods in time domain using MATLAB software. Surge motion equation of TLP is highly nonlinear because of large displacement and it should be solved with large perturbation parameter in time domain. In this paper, homotopy perturbation method (HPM) is used to solve highly nonlinear differential equation of surge motion. Also the numerical methods such as modified Euler method (MEM) and MATLAB are used to solve the ordinary differential equation of motion. MEM is used for highly nonlinear Duffing type equation of surge motion of TLP, whereas the nonlinear part is not considered in MATLAB solution. Calculated responses by analytical HPM are compared with those obtained from both MEM and MATLAB responses. © 2017, JASNAOE.