The mechanical properties of early‐age fly ash (FA) concrete was experimentally studied. The splitting tensile strength and compressive strength under different curing ages, temperatures, cooling methods and FA contents were analyzed. The experimental results showed that the splitting tensile strength of concrete increased proportionally with temperature in the early stage and decreased as the temperature further increased. Compared to the concrete with FA content of 10% and 30%, the compressive strength of concrete with FA content of 20% was found to be highest at the age of 90d. The strength of the specimens under water cooling was comparatively lower than that under air cooling. The compressive strength of FA concrete heated to 150°C was greater than that of the unheated concrete. The compressive strength of FA concrete heated to 550°C was lower than that of concrete without treatment at high temperature. After high temperature exposure at the age of 90d, the compressive strength of the specimen was higher than that of the specimens at the ages of 7d, 14d and 28d. The microstructures of the specimens aged 90 days were measured by the SEM method before and after being exposed to high temperatures.