In this article it is studied to prepare nanoparticle of aluminum fluxes for brazing aluminum and its alloy. The operation is convenient and the diameter of the nanoparticle can be controlled. The thermodynamics performance and dynamics performance of the system are both steady. The method is feasible and applied. It is studied to prepare a series of KF-AlF 3 eutectic products at various eutectic conditions. The melting points of the products are measured by differential thermal analysis (DTA) and the composites of each product are conformed by X-ray diffraction. It is suggested that it is good to get the ideal fluxes consisted of KAlF 4-K 3AlF 6 at a certain temperature. The KAlF 4-K 3AlF 6 eutectic nanoparticle is prepared by microemulsion method. It is suggested by X-ray diffraction patterns that material of the main phase is KAlF 4 and the material of the minor phase is K 3AlF 6. The melting point of nano-eutectic is 560 ℃ proved by differential thermal analysis. The material is considered as the perfect aluminum fluxes for brazing aluminum and its alloy.