This invention discloses n,n'-bi(inter cresyl) urea water phase high pressure preparation method. 1) m-toluidine is mixed with water, then mineral acid is added for salifying reaction, then urea is added and agitated, there equivalence ratio is 1:0.95-1.05, mol ratio of the m-toluidine and urea is 1:0.5-1, the salifying reaction temperature is 0-80 degree centigrade. 2) the reaction liquor above is added into high pressure kettle, pressure of the kettle reaches 2-10atm, and keeps 1-5 hours, then material is out, separated and washed. Comparing to existing preparation method, the material price is low and easy to get, reaction is simple, workshop operability is high, the whole yield and manufacture cost is low, so it is propitious to industrial manufacture. Computer by m-toluidine, the product mol yield can reach more than 90 percent of the theoretical value, if mother liquor is nest after reaction, the mol yield can reach more than 95 percent.