The invention provides a preparing method of three-dimensional porous nickel foam. The preparing method comprises the following steps that activating is conducted on foamed nickel sheets in an activating liquid, and the activating liquid comprises a mixed liquid of palladium chloride and hydrochloric acid; and the activated foamed nickel sheets are put into the mixed liquid for being soaked to obtain the three-dimensional porous nickel foam, and the mixed liquid comprises trisodium citrate, nickel sulfate, boric acid, sodium hypophosphite, 2,4,7,9-tetramethyl-5-decyne-4,7-glycol, hexadecyl trimethyl ammonium bromide and triethanolamine. The preparing method is simpler compared with technologies such as a template method, a dealloying method and an electrodeposition method, and is low in energy consumption, low in cost and easy in scale production, and the prepared porous nickel foam is a penetrating circular hole with 1-5 microns.