A method and device for manufacturing fertilizer through processing phosphoric acid mixed acid liquid waste.W When mixed acid liquid (fatigue liquid) containing phosphoric acid, nitric acid and ethanoic acid in high concentration and generated in the etching process of aluminum, after measurement of phosphoric acid and nitric acid in the mixed acid liquid, calculated Diammonium phosphate (NH4)2HPO4 is added based on the measurement, so that the phosphoric acid and the nitric acid react. The phosphoric acid and the nitric acid are recovered to obtain ammonium dihydrogen phosphate; NH4H2PO4 as fertilizers. The processing device comprises a solid-liquid mixing reactor with a heat mechanism and a mixture stirring mechanism, a measurement injection device used for measuring and injecting liquid waste, a powder injection device and a control mechanism.
