The invention provides rare earth ion doped lanthanum orthovanadate nanocrystals as well as a preparation method and an anti-counterfeiting application thereof and belongs to the technical field of fluorescent nano materials. The preparation method comprises steps as follows: sodium orthovanadate is taken as a vanadic acid source, rare earth chlorate is taken as a rare earth ion source and is lanthanum chloride, europium chloride or dysprosium chloride, polyacrylic acid is taken as a surfactant, water serves as a solvent, pH is adjusted, the raw materials react in a microwave reactor with polytetrafluoroethylene as a lining, centrifugal separation and washing are performed after the reaction, and the rare earth ion doped lanthanum orthovanadate nanocrystals are obtained. The method adopts a simple and convenient process, is low in cost, environment-friendly and good in process repeatability and takes short time; the obtained nanoparticles have good water solubility, uniform particle size and high fluorescent efficiency; the rare earth ion doped lanthanum orthovanadate nanocrystalline water solution can be directly used for printing and writing as fluorescent anti-counterfeit ink.