The invention discloses a method for preparing an anti-scaling coating on the surface of a large water ring vacuum pump impeller. Firstly, the impeller of the large water ring vacuum pump is separately blasted and conventionally ultrasonically cleaned and then is blow-dried with a gas cylinder. A titanium dioxide ethanol solution is prepared by mixing an anhydrous ethanol and titanium dioxide powder, in a supercritical carbon dioxide reactor, the titanium dioxide ethanol solution is added to raise the temperature and pressure to 80 DEG C and 10 MPa respectively, so that the titanium dioxide ethanol solution is uniformly dispersed in the supercritical carbon dioxide, a nozzle of the reactor is opened, the titanium dioxide ethanol solution is sprayed into a high temperature zone of a directcurrent plasma torch, a solvent in tiny droplets rapidly evaporates under high temperature and high speed environment, titanium dioxide nanoparticles are precipitated and rapidly melted into titaniumdioxide droplets, and the titanium dioxide anti-scaling coating with a layered structure is obtained.