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The Paired-Column Semi-Submersible (PC Semi) is a concept design by Houston Offshore Engineering (HOE). It distinguished from conventional semi-submersibles from three aspects: eight columns rather than four, rectangular columns rather than square and larger column slenderness. The current study numerically investigate the flow around a fixed PC-Semi at different velocities and current headings. The finite volume CFD solver naoe-FOAM-SJTU is utilized. Turbulence flow around the semi-submersible is modeled by Shear-stress transport based delayed detached-eddy simulation (SST-DDES). The present computation results are compared with existing experimental and numerical results. To illustrate the benefit of SST-DDES model, an extra unsteady Reynolds-Average Navier-Stokes (URANS) simulation using the same SST model is performed. Pressure and viscous forces on difference columns are analyzed. Time-averaged and instantaneous flow visualizations are given. In addition, free-surface effect are also discussed. This preliminary study show comprehensive wake interactions between columns and provide a better understanding of Vortex-Induced Motions (VIM) mechanism of multi-column offshore structures.