Abstract: Mass eccentricity and stiffness eccentricity are two key forms of asymmetric structures. Based on the general dynamic equation of one-storey asymmetric offshore platform subjected to wave and earthquake loadings, the vibration equation considering different eccentricity forms is deduced in this paper. At different water depths, the performances of asymmetric platforms subjected to earthquake load, wave load, or simultaneously both, are numerically analyzed. The torsionally coupled effects are studied considering the variation in eccentricity form, eccentric ratio and target component’s location. In addition, the influence of environmental action intensity on torsionally coupled effect is analyzed. The numerical results show that eccentricity form, eccentric ratio and target position have non-negligible influence on torsionally coupled effects. Furthermore, the influences of combined environmental actions are different for asymmetric platforms with different periods or in different foundation conditions.