The reaction course of urea synthesis from NH3 and CO2 was discussed on the basis Of bimolecular reaction mode. It was considered probable that amino-formic acid is a vigorously corrosive intermediate product. An electrochemical corrosion mechanism of stainless steels and titanium in the urea medium was proposed. The reaction course of urea synthesis from NH3 and CO2 was discussed on the basis of bimolecular reaction mode. It was considered probable that amino-formic acid is a vigorously corrosive intermediate product. An electrochemical corrosion mechanism of stainless steels and titanium in the urea medium was proposed.