As a key component of airstream system equipped in the road sweeper, the structure of the suction nozzle determines its internal flow field distribution, which affects the dust-sucking efficiency to a great degree. This research is aiming to determine a better suction nozzle structure. Starting with an analysis of the one used in a certain type of road sweeper, the initial model of the suction nozzle is established, and the internal flow field is simulated with typical computational fluid dynamics (CFD) software named FLUENT. Based on the simulation results, the dust-sucking capability of the initial structure is evaluated from the aspects of pressure and velocity distribution. Furthermore, in order to explore the influence of different structural parameters on the flow field distribution within the suction nozzle, models with different cavity heights and shoulder angles are established, and Univariate Method is utilized to analyze the contrast models. The model with chamfering is also studied in the same way. Based on these simulation results, an optimized scheme of the initial structure is proposed. Moreover, the simulation of two-phase flow in the optimized structure is completed on the basis of discrete phase model (DPM), the particle trajectory is tracked and the result shows a significantly better dust-sucking effect with a more reasonable pressure field and velocity field in comparison with the initial model. Through present researches, the structure of the suction nozzle is expected to be improved, and it also provides a design reference for the development of high efficiency road sweepers.