In this paper, the process of the introduction of numerical diffusion is investigated when low‐order differential scheme in convection‐diffusion equation for discrete suspended load is in use. According to the results of instances calculation, the optimal choice for parameters when physical diffusion is simulated by numerical diffusion is obtained. Finally, comparison between several commonly used low‐order schemes is conducted and the most viable low‐order scheme in simulating physical diffusion by numerical diffusion is proposed in dealing with suspended load.