The influence of heat pre-treated temperature(600℃、 700 ℃、 800℃ and 900 ℃) on washing pre-treated MSWI fly ash(PW-MSWI) cementitious activity was studied by mortar experiment.Concrete experiment was also conducted to figure out the influence of both PW-MSWI and heat pre-treated PW-MSWI(PWH-MSWI) on concrete strength development.Hydration mechanism and products of cement-MSWI cementitious system were analyzed by XRD and DSC-TG.The results show that heat pre-treatment improve the early-age activity, but reduce the later-age activity of PW-MSWI.The best heat pre-treated temperature is 700℃.Both PW-MSWI and PWH-MSWI improve the early-age strength, but harmful to later strength development of concrete.PWH-MSWI is better on concrete early strength improvement than PW-MSWI.In contrast to cement, more ettringite and chemical bonding water are formed during the early-age hydration of cement-MSWI cementitious system, but the hydration rate of ettringite and calcium hydroxide slow down in later age, leading to less chemical bonding water.