The hydration and water resistance of gypsum slag cement with different contents of calcined phosphogypsum（CPG） were investigated in terms of the tests of setting time， fluidity， pH value of pore solution， flexural strength， compressive strength， water absorption， softening coefficient， hydration heat and hydration products analysis. The results indicate that the setting time of gypsum slag cement is shortened， the fluidity is reduced， and the water absorption and cumulative heat release at 3 d are increased with the increase of CPG. The pH value of pore solution of cement paste decreases fast at early hydration， but shows stable at the age of 56 d. As the CPG content increases from 40% to 70%， the pH value of pore solution of cement paste decreases from 11.02 to 10.62， the softening coefficient of cement mortar decreases from 0.98 to 0.91. The main crystalline products are gypsum and ettringite， in which the ettringite content decreases with the increase of CPG.