We design a multi-mode multiplexer/de-multiplexer based on parallel mode couplers. The multi-mode multiplexer/de-multiplexer consists of two single mode fibers and a few-mode fiber. According to the effective refractive index matching principle, the parameters of fiber are determined. The influence of different core distances on the performance of multi-mode multiplexer/de-multiplexer is analyzed, and the optimum core distance is determined. The working wavelength bandwidth corresponding to the multi-mode multiplexer/de-multiplexer is analyzed. Simulation results show that the multi-mode multiplexer/de-multiplexer can achieve the multiplexing of LP01, LP11 and LP02 modes without the need of a mode converter, the optimal coupling length is 4530 μm, and the wavelength bandwidth is 60 nm.