The invention discloses a simple preparation method of an electrochemiluminescent reagent ruthenium polypyridine complex. The preparation method comprises the following steps: dissolving a ruthenium chloride hydrate and 2, 2'-dipyridyl in a mixed solvent of ethanol and ethylene glycol, wherein the ratio of ruthenium trichloride in the ruthenium chloride hydrate to 2, 2'-dipyridylis 1:4-1:5, and the concentration of ruthenium trichloride in the mixed solvent is 0.02-0.025mol/L; heating to react, wherein the reaction temperature is 70-100 DEG C and the reaction time is 6-10 hours; cooling to room temperature and carrying out rotary evaporation to remove ethanol; adding a saturated sodium chloride solution to separate out solids, filtering, adding water to recrystallize and drying to obtain tri(2, 2'-dipyridyl) ruthenium chloride (II) hexahydrate. The synthetic method is simple and convenient, short in reaction step, easy to operate, less in consumption of organic solvents, simple in post-treatment and high in product purity. The conversation ratio of noble metal ruthenium reaches up to 95%, so that the preparation method is less in environmental protection pressure and convenient for industrialized production.