Five geometrically similar nitration reactors filled with polystyrene and water as mediums were used to simulate the rules of residence time distribution（RTD）of the fluid and that of reactor scale-up. The experimental results show that the optimum pilot volume of solid-liquid phase nitration reactor is 0.040 m³. The relevant empirical formula of scale-up is obtained thereof, which can be used as theoretical and experimental reference for the further investigation.