Abstract: The action mechanism of high titanium blast furnace (BF) slag in concrete was studied by XRD、 DTA、 SEM and determining the combine-water amount of hydration process. The results show that the high titanium blast furnace slag mixed in the concrete can help concrete to form microcosmic compact deposit, accelerate the hydration rate of cement, produce "the second reaction", advance the strength of concrete. "The second reaction" of high titanium blast furnace slag takes place at the later stage of hydration. When mix right amount of exciting agent in high titanium blast furnace slag, it can accelerate the "the second reaction" to progress.