This paper describes the results of study on compressive strength developments of fly-ash concrete in standard curing. The 28-day compressive strength of fly-ash concrete is reduced as the ratio of cement replaced with fly-ash. However, the compressive strength of fly-ash concrete increases rapidly since 28 days. On the basis of the above, I was able to suggest the coefficient S of the prediction equation of compressive strength of fly-ash concrete about CEB-FIP1990 model cord.