Pressure drop characteristic experiments are one of the main means to obtain the hydraulic characteristics of complex structural components in the development of advanced reactors. Some advanced research reactors employ high-temperature liquid sodium, lead, and molten salts as coolants, using the high-temperature original fluid to carry out pressure drop characteristic experiments has a lengthy construction period and high operating costs, and the applicable measurement approaches and instruments are restricted, which is detrimental to obtaining experimental data to support the development of advanced reactors efficiently and promptly. Water, which is more frequently utilized, features more mature measurement methods and is more optically transparent; however, its physical properties significantly differ from those of the original fluid. If water can substitute the original fluid for conducting pressure drop characteristic experiments, it will considerably shorten the experimental period and reduce the experimental cost. Based on the basic principles of similarity theory modeling analysis, this study conducted a research on the similarity modeling criteria for pressure drop characteristic experiments, and obtained that Re is the similarity criterion number that needs to be followed in pressure drop experiments. Through numerical simulation and experimental methods, the pressure drop characteristics of a complex structural component under different working fluid conditions of lead bismuth and water were compared. The results showed that the pressure drop characteristics of the same structural component under Reynolds numbers of lead bismuth and water were consistent, verifying the feasibility of using Re criterion to conduct pressure drop characteristic experiments on complex structural components through alternative fluids.