To investigate the wake interference effects and flow control mechanisms, we conduct two-dimensional direct numerical simulations (DNS) of two side-by-side counter-rotating cylinders. The OpenFOAM pimpleFoam solver is employed to analyze wake characteristics, lift and drag coefficients, and variations in the velocity field under different gap ratios and rotational speed ratios. The results show that the wake exhibits five typical modes: irregular vortex shedding, single bluff-body shedding, in-phase vortex shedding, out-of-phase vortex shedding, and steady flow. Under outward counter-rotation, the critical rotational speed ratio of the wake decreases as the gap ratio increases. In contrast, for inward counter-rotation, the critical speed ratio increases, with both conditions ultimately approaching the critical speed ratio of a single cylinder. Through potential flow theory, the study reveals the mechanism of wake reversal and the formation of virtual elliptical flow lines around the cylinders during inward counter-rotation. These findings provide a theoretical foundation for the application of counter-rotating cylinders in flow control, particularly in marine and aerospace engineering.