The effects of replacement ratio of recycled coarse aggregate （RCA）， fly ash content and initial moisture content of RCA on the moisture absorption process of recycled concrete were studied by experiments. The results show that the capillary water absorption coefficient and humidity response rate of concrete with the 25% replacement rate of RCA are the smallest， and those of concrete with a replacement rate of 0%， 50%， 75%， 100% increase in above rate sequence. The capillary water absorption coefficient and humidity response rate of concrete with the fly ash content of 10% are the smallest， and those of concrete with the fly ash content of 0%， 20%， 30% also increase in above rate sequence. The capillary water absorption coefficient and humidity response rate of concrete increase with the increase of initial moisture content of RCA. In the early stage of the humidity response， the three influencing factors have a greater effect on the concrete humidity response. As the humidity response progresses， the effect gradually decreases. And with the increase of fly ash content and initial moisture content， the difference in the humidity response rate of concrete in different periods increases. Finally， based on the basic theory of the mass transfer in concrete， the moisture diffusion coefficient of recycled concrete under different test conditions is calculated by using the experimental data. Then， the prediction model of the humidity response of recycled concrete is established.