Taking the ultra-fine sand concrete of Chittagong project in Bangladesh as the research object,we study different influencing factors on the age strength of plain concrete,such as the sand ratio,the fineness modulus of sand and the dosage of water reducing agent.The results show that the strength of ultra-fine sand concrete increases rapidly and then increases slowly with the age,3 d strength reaches more than 55% of 28 d strength,7 d strength reaches more than 70% of 28 d strength.The effect of small increase of sand ratio is not significant to the age strength.28 d strength of medium sand concrete is slightly smaller than that of the ultra-fine sand concrete.When the dosage of water reducing agent exceeds 1%,28 d strength is greatly improves.