Flow past cylinders is an important issue in ocean engineering. Periodical vortex shedding occurring around the offshore platform in current leads to reciprocating motion of the offshore platform, which may aggravate the fatigue damage and thus cause the reduction of fatigue life of the moorings. In order to study the mechanical characteristics of flow past multi-column floating wind turbine platform and understand the mechanism of wake interference clearly, numerical simulations were performed using Delayed Detached Eddy Simulation (DDES). The effects of headings and current velocities on the mechanical characteristics of the semi-submersible floating wind turbine platform were investigated. The mechanism of wake interference was studied from the level of coherent structures, and spatial correlation between different wakes behind the columns was also investigated. The results demonstrate that: (1) the average drag force coefficient of downstream column has a large fluctuation with the change of current velocity; and streamwise vortex and hairpin vortex are the main coherent structures; (2) the interaction between coherent structures results in wake interference; (3) the upstream wake and the downstream wake have strong spatial correlation, but their coherent structures are different. The research results provide a theoretical reference for understanding the phenomenon of flow past multi-column offshore platform.