By means of hydration heat,XRD and SEM,effect of phosphorus and fluorine(P_2O_5 and F~-)in phosphorous slag on hydration process of tricalcium silicate(C_3S)and tricalcium aluminate(C_3A)was explored.The results indicated that the early hydration exothermic rate of C_3S and C_3A was obviously lowered by P_2O_5 and F~-in phosphorous slag,the second peak occurring time of C_3A was delayed by 0.9 h,the exothermal output of C_3S was reduced by 25.04% and the time of accelerating stage was postponed by 0.86 h.The early hydration degree of C_3S and C_3A was also decreased.Due to the influence of P_2O_5 and F~-,more pores and thinner crystals can be observed in the microstructure of hardened paste and the chance of cracks was reduced. By means of hydration heat, XRD and SEM, effect of phosphorus and fluorine (P_2O_5 and F ~ -) in phosphorous slag on hydration process of tricalcium silicate (C_3S) and tricalcium aluminate (C_3A) was explored.The results indicated that the early hydration exothermic rate of C_3S and C_3A was delayed by 0.9 h, the exothermal output of C_3S was reduced by 25.04% and the time of accelerating stage was postponed by 0.86 h. The early hydration degree of C_3S and C_3A was also decreased. Due to the influence of P_2O_5 and F ~ - more pores and thinner crystals can be observed in the microstructure of hardened paste and the chance of cracks was reduced.