In this study, numerical analysis has been carried out to investigate the hydrodynamic interactions of two multi-columns platforms. The objective of the work is to preliminarily evaluate the feasibility of a tension-leg-platform (TLP) dry tree unit (DTU) with tender assisted drilling (TAD) from the aspect of vortex-induced motions, characterized by the current. Two multi-columns floating platforms with a small gap ratio (28% of the overall platform width) are numerically simulated with the scenario of 3 degree-of-freedom (DOF) on the horizontal plane (including transverse, in-line and yaw motions). A comprehensive numerical simulation was conducted to examine the hydrodynamics interactions due to the flow over two floating platforms. Horizontal plane motions including transverse, in-line and yaw motions as well as drag and lift forces on both structures are discussed. The numerical data on the multi-body VIM interactions within the “lock-in” region will serve as a preliminary study for future coupled motions analysis of the TLP-TAD system design.