The invention provides a method for recovering rare noble metal from waste water slag of a process of producing silver and selenium. The recovering steps are as follows: a. adding the waste water slag of the process of producing silver and selenium into a reaction kettle, adding a sulfuric acid solution to make a slag to liquid ration 5-5.5, reacting for 30-60 min at a room temperature with stirring, settling for 5-24 hours at the room temperature, and filtering after the settlement to obtain leaching slag enriched with selenium noble metal and a leaching solution with a small amount of residual noble metal, the leaching solution being for use in the next step; and b. putting the leaching solution with the small amount of the residual noble metal in the reaction kettle; heating to a temperature of 80-95 DEG C, adding discharge waste liquid produced by sodium sulfite desulfurization in the production process of the rare noble metal, wherein the adding amount of a precipitant is 1.1-1.3 times that of a theoretical usage amount of Cu2+ ions in the leaching solution with the small amount of the residual noble metal, reacting for 30-120 min at the temperature of 80-95 DEG C, and filtering to obtain cuprous sulfide slag and a solution after the reaction. The method is simple in process flow and circularly economic in waste utilization, and has low production cost and high metal recovery rate.