The invention relates to a decontamination research device for a nuclear reactor plant, in particular to a testing apparatus for simulating out-of-reactor decontamination research of sodium attached equipment of a fast reactor to solve the outer-of-reactor decontamination research problem of the sodium attached equipment of the fast reactor in China. The testing apparatus comprises a solution preparation tank, a decontamination tank, a waste liquid tank, a vacuum pump, a circulating pump and a temperature controller, wherein the top of the decontamination tank is lower than the bottom of the solution preparation tank; the top of the waste liquid tank is lower than the bottom of the decontamination tank. The testing device has wide applicability, can be used for developing decontamination method test research on various kinds of sodium attached equipment and has the advantages of high safety and reliability, low building expense, convenience in operation, easiness in recovery of waste liquids and the like, the variety of decontaminant, decontamination temperature, decontamination time, the flow speed of the decontaminant and other conditions can be selected conveniently, and the problem about out-of-reactor decontamination research on the sodium attached equipment of the fast reactor in China is solved effectively.