By evaporable water test and compressive strength test, this paper studies on the influence of lime dust on pore structure and compressive strength of fly ash-cement paste. The test results show that: 1) With the volume of lime dust as cement replacement increasing, porosity and big pore to total volume ratio of fly ash-cement paste are gradually raising .However, with the volume of lime dust as fly ash replacement increasing, porosity of fly ash-cement paste decreases gradually, while big pore to total volume ratio firstly increases, and then decreases. 2) Substituting lime dust for isometric cement, compressive strength of fly ash-cement paste containing over 5% lime dust reduces gradually when the proportion of lime dust replacing cement raises. Whereas, substituting lime dust for isometric fly ash, the influence of lime dust content on compressive strength of fly ash-cement paste within less than 6% lime dust is not obvious. But When lime dust content is 9%, the compression strength of fly ash-cement paste increases by 20.0% around.