The setting times and compressive strength of Portland cement pastes containing amino trimethy lene phosphonic acid(ATMP) were tested. By means of hydration heat measurement, X ray diffraction(XRD) analysis, differential thermal gravity(DTG) analysis, scanning electron microscope(SEM) analysis and Zeta potential test, the effects of ATMP on hydration of cement were investigated, and the retarding mechanism of ATMP on cement pastes was discussed. The results show that with the increase of use level (the mass percentage of cement) of ATMP, the setting time of cement pastes is gradually extended. Compared with the blank sample, the 3d compressive strength of cement pastes is reduced only when the use level of ATMP is greater than or equal to 008%, and the 28d compressive strength is increased when the use level of ATMP is ranging in 010%. In the initial stage of cement hydration, ATMP accelerates the hydration of C3A minerals. ATMP can chelate Ca2+ in the cement pastes to form sparingly soluble Ca35(C3H7O10NP3) chelation, and the chelation wraps on the surfaces of the unhydrated cement particles, which retards further hydration of C3S minerals and formation of Ca(OH)2, resulting in significant decreases in the hydration heat and hydration heat evolution rate of cement with the addition of ATMP.