In this paper, a dual-core mode converter based on directional couplers is presented, which can achieve the conversion from the fundamental-order mode (LP₀₁ mode) to the high-order mode (LP₁₁ mode). The theoretical analysis model of the dual-core mode converter is built by the finite element and beam propagation methods to explore the influence of optical fiber parameters on the conversion performance. Numerical simulations reveal that the bandwidth of this mode converter can reach 320 nm when the extinction ratio is greater than 20 dB, and its conversion rate is 99.7% when the bandwidth reaches 400 nm, and the extinction ratio is greater than 10 dB. Compared with the traditional mode converter, the proposed converter features a simple structure, a high conversion rate, and wide bandwidth. Therefore, it is suitable for applications in optical communication systems.