Abstract: According to the basic features of seabed gas hydrate and the multiphase flow theory, by comparing separation schemes, this paper accomplished the preliminary design of the structural parameters for the hydrocyclone. As the original Hancock overall efficiency formula could not be directly used in the calculation of the separation efficiency of seabed gas hydrate mixed slurry, the definition of parameters of the original formula was modified to work out an improved formula. Then, the finite element model for the hydrocyclone was established and developed, based on the Reynolds stress model, a flow field simulation analysis method applicable for the liquid-solid-solid tri-phase flow, and by simulation analysis of the numerical value, distribution rules of parameters of the hydrocyclone such as the internal speed, pressure and density are obtained. Finally, the optimal structural parameter combination for the hydrocyclone was worked out by optimizing the structural parameters through orthogonal test, thus increasing the separation efficiency by 36. 24%, compared with the initial scheme. Then, the operational parameters were further optimized through orthogonal test to gain an optimal operational parameter combination for the hydrocyclone, increasing separation efficiency of the hydrocyclone by another 5. 15%.