The invention relates to a method for producing a washing machine tank cleaning agent, and the method is as foillows: mixing sodium percarbonate, lauryl sodium sulfate and fatty alcohol-polyoxyethylene ether for stirring to obtain a mixture; heating the mixture to 80-95 DEG c, wherein the heating time is 1-3 hours, then adding sodium carbonate, bicarbonate and methylisothiazolinone, continuously heating to 95-120 DEG c, wherein the heating time is 40-50 minutes, cooling to room temperature, then adding EDTA (ethylene diamine tetraacetic acid)-tetrasodium, sodium metasilicate pentahydrate and pancreatic bio-enzyme, continuously stirring and heating to 50-75 DEG c, wherein the heating time is 30-40 minutes, and then preparing the granular or powdery finished product according to a conventional technical method. The washing machine tank cleaning agnet integrates cleaning, descaling, antibacterial, anti-dirting, re-deposition and other functions, and is good in washing performance, easy tobiologically degrade, environment-friendly and capable of effectively cleaning, stripping and decomposing dirt, fiber, impurities, bacteria and other pollutants accumulated in a washing machine, so that secondary pollution of the washing machine is avoided.