The present invention relates to a preparation method for electrolyte of vanadum oxidation-reduction liquid stream. It contains 1, putting weight ratio 1.5-2.5 :1 vanadium trioxide and vanadium pentoxide powder in furnace and calcination at 200-700 degree centigrade, to make yellow powder became black powder to obtain multivalent vanadum compound, wherein quadravalence vanadum greater than total vanadum by 50 per cent, 2, adding distilled water in specific gravity 1.84 concentrated sulfuric acid to proceed 2 : 1 diluting then adding above-mentioned compound, according to mass fraction preparation to 65-75 per cent concentration vanadyl sulfate solution, wherein total vanadum concentration in 25-45 per cent, 3, adding 1-10 per cent concentration alkali salt or alkali salt and alkaline earth metal salt. Said invention adds additive in vanadyl sulfate solution, which not only raising vanadum ion solubility, preferably solving crystallizing jamming battery flow field problem in charge discharge process, but also reducing vanadium ion osmotic problem in film, greatly raising battery energy source efficiency.