NOVELTY - Recovering N-(phosphonomethyl)iminodiacetic acid (PMIDA) from its production waste water in order to prepare glyphosate, comprises adjusting the amount of PMIDA in waste water, adding hydrogen peroxide, adjusting the pH, transferring the waste water from a triple-effect evaporation system to an evaporator and transferring evaporated acidic water to a biological treatment system, transferring the contents of the evaporator to a centrifuge and centrifuging to obtain a solid industrial salt and primary mother liquor and transferring the primary mother liquor to the evaporator.    USE - Recovering N-(phosphonomethyl)iminodiacetic acid (PMIDA) from its production waste water in order to prepare glyphosate (claimed), used for agriculture, forestry, industrial traffic industry, comprising a forest, rubber garden and farmland, orchard, sugarcane field of railway and airport for weeding.    ADVANTAGE - The method not only can solve the PMIDA recycling, but also capable of treating waste water of N-(phosphonomethyl)iminodiacetic acid so as to make the phosphorus content in the waste water, waste water discharging meets the national standard; simple operation, reduces the raw material, saves investment and reduces cost and reduces pollution.    DETAILED DESCRIPTION - Recovering N-(phosphonomethyl)iminodiacetic acid (PMIDA) from its production waste water in order to prepare glyphosate, comprises:    (1) adjusting the weight percent of PMIDA in its production waste water to 0.7-1.5% and adding hydrogen peroxide to remove formaldehyde;    (2) adjusting the pH of treated wastewater to 4.5-6.0 in a neutralization reactor, transferring the waste water from a triple-effect evaporation system to an evaporator and transferring evaporated acidic water to a biological treatment system;    (3) transferring the contents of the evaporator to a centrifuge, and centrifuging to obtain a solid industrial salt and primary mother liquor;    (4) transferring the primary mother liquor to the evaporator, using hydrochloric acid for adjusting the pH to 1.3-1.8, evaporating and concentrating under a negative pressure, and separating a solid industrial salt from a PMIDA solution;    (5) evaporating, concentrating, and desalting the PMIDA solution until the PMIDA content in the mother liquor is greater than 15%;    (6) adding hydrogen peroxide dropwise to an oxidation reactor for glyphosate production, oxidizing, adding ferrous sulfate dropwise to a reduction reactor and preparing an aqueous glyphosate solution, and    (7) subjecting the aqueous glyphosate solution to mechanical membrane separation, and then adding glyphosate to obtain the aqueous glyphosate solution of a required concentration.