In order to obtain the critical use level（wFA,c） of fly ash for concrete of various water binder ratios（mW/mB） of 036060 under the promise of ensuring the carbonization durability of concrete, the carbonization depths of concretes with mW/mB of 036,043,050 and different use level（wFA） of fly ash of 0%, 20%, 40%, 60%，and with mW/mB of 060,use level of fly ash of 0% were tested, respectively. The accelerated carbonation tests were carried out under the condition of controlled CO2 volume fraction（20±3）%, temperature （20±2）℃ and relative humidity （70±5）%. Concrete specimens should be natural curing for 7d, in which the daily average temperature is 128℃. In addition, the effects of mW/mB and use level of fly ash on the carbonization of concrete were quantitative analyzed, and the mathematical model to describe the relationship between the critical use level of fly ash and mW/mB for 20mm carbonation depth was established. The experimental results show that the carbonation depth of concrete with different mW/mB increases with increasing the use level of fly ash. The use level of fly ash more than 20% has significant improvement on the carbonation rate. Moreover, the carbonization durability of concrete obviously decreases with increasing mW/mB. The mathematical model to describe the relationship between the critical use level of fly ash and mW/mB for 20mm carbonation depth is:wFA,c=1748-2809 mW/mB. Based on the mathematical model, the critical use level of fly ash which can ensure the carbonation durability of concrete can be calculated in a certain mW/mB.