In order to study the effects of the spacing of nozzles on the dilution efficiency of a multi-hole diffuser, the realizable k-ε model of the Computational Fluid Dynamics(CFD)software Fluent was used to simulate the effective cross-flow velocity, the jet concentration trajectory, the velocity field, and the concentration field of two tandem jets in cross-flow with different spacing. The results show that, as the spacing of nozzles increases, the sheltering effect of the first jet weakens, the effective cross-flow velocity increases, and the degree of curvature of the jet concentration trajectory increases. Near the jet, there is an exponential relationship between the concentration trajectory and the distance downstream of the nozzle with an exponent of 1/2, and an exponential relationship between the concentration trajectory and the spacing of nozzles with an exponent of -0. 27. At more distance from the jet, there is an exponential relationship between the concentration trajectory and the distance downstream of the nozzle with an exponent of 1/3, and an exponential relationship between the concentration trajectory and the spacing of nozzles with an exponent of -0. 18. The spacing of jets has little influence on the concentration of the first jet. However, the concentration of the second jet decays faster in the direction of flow when the spacing of nozzles decreases, and the concentration grows more stable when the distance from the nozzle is greater than eight times the nozzle diameter.