The invention discloses a method for pretreating wastewater generated in the production of N-(Phosphonomethyl) iminodiaceticacid (PMIDA). The method comprises the following steps: (1), recovering N-(Phosphonomethyl) iminodiaceticacid (PMIDA) by adopting an acidification process; and (2), after catalytic alkaline hydrolysis and stripping deamination, recovering aqueous ammonia, removing formaldehyde and decomposing organic phosphorus in wastewater into inorganic phosphorus. The pretreating method is simple to operate and low in cost, the useful substances in wastewater can be effectively recovered, the load of organic pollutants difficult to degrade in wastewater can be reduced, and the biochemical feasibility of wastewater can be enhanced; and the COD (chemical oxygen demand) removal rate of the pretreated wastewater generated in the production of N-(Phosphonomethyl) iminodiaceticacid (PMIDA) is higher than 72 percent, the removal rate of organic phosphorus is higher than 95 percent, the removal rate of inorganic phosphorus is higher than 99.9 percent, the removal rate of formaldehyde is higher than 95 percent, the biochemical feasibility of wastewater is remarkably enhanced, and the B/C value is improved to 0.4 from 0.1.