In order to study the hydration characteristics of alkali activated phosphorous slag composite cementitious materials, the composition and microstructure characteristics of hydration products of phosphorus slag activated by Ca(OH)2, gypsum and cement phosphorus slag mixture were studied by X ray diffraction(XRD), thermogravimetry differential scanning calorimetry(DTA TG) and scanning electron microscope(SEM). The results show that the potential activity of phosphorus slag can be well exerted in the excitation of Ca(OH)2, and its activity gradually increases with the increase of specific surface area and the prolongation of age;the potential activity of phosphorus slag can be exerted in advance to improve its hydration process in the excitation of Ca(OH)2 and gypsum;phosphorous slag can improve the degree of cement hydration, and the larger the specific surface area and the longer the age, the more significant the promotion of cement hydration degree.