The vortex diode is a key candidate for the equipment of the passive safety system of the molten salt reactor. Experimental studies to determine the diodicity (ratio of reverse flow Euler number to the forward flow Euler number at the same Reynolds number) using high-temperature molten salt are strongly limited because of the huge technical effort and financial requirements for such studies; moreover, possible solutions that involve a scaling method that uses surrogate fluid to obtain the diodicity must be validated. To determine the diodicity and verify the scaling method, an experiment using one kind of heat transfer oil (Dowtherm-a) as the surrogate fluid was carried out. In addition, a computational fluid dynamics (CFD) simulation method was also adopted to study the flow characteristics in the vortex diode using three different fluids. The results show the following: it is feasible to study the diodicity of a vortex diode by a scaling experimental method using surrogate fluid, the CFD simulation method established in this paper can be applied to study the diodicity of the vortex diode, and the structure of the flow field and velocity distribution in the vortex chamber for reverse flow are independent of fluids and only related to the Reynolds number.