The present invention provides a method having no need of any chemical oxidant to prepare solid K2FeO4. It is characterized by that using diaphragm-type electrolytic bath and using DC to make electrolysis in the KOH solution containing stabilizer, and make the electrode containing iron material undergo the process of anodic oxidation to directly obtain the invented solid K2FeO4 whose purity is greater than 90 wt% by means of one step. Said solid K2FeO4 is applicable to make treatment agent for sewage or drinking water and oxidant for organic synthesis. After having been purified it also can be used as positive active substance of alkaline perferrate cell.