Abstract: The mechanical properties of concrete are affected by the humidity, and the hydraulic concrete usually has the characteristics of wet expansion. Because of the large water contact area and long water conveyance time, the internal humidity change in the concrete thin-walled aqueduct will affect its working performance. Based on Fick's second law, a humidity diffusion model is established, and the concrete saturated humidity diffusion coefficient is calibrated by using a physical model. Considering the variation of concrete elastic modulus with humidity and the effects of the wet expansion, an analytical model of the humidity field and stress field of the aqueduct is established to analyze the influences of different diffusion depths of humidity along the aqueduct wall thickness on the deformation and internal force performance of the aqueduct. The analysis results show that with the increase of water transfer time, the diffusion depth is non-uniformly distributed along the wall thickness of the aqueduct, and the diffusion depth of the humidity will affect the deformation and stress distribution of the aqueduct. With the increase of the humidity diffusion depth of the aqueduct wall, the longitudinal deflection of the aqueduct increases, the transverse deformation decreases, and the transverse influence is greater than that of the longitudinal effect. The compressive stress on the inner side of the aqueduct wall increases and the outer tensile stress increases because of the increase in humidity. The humidity is favorable for the aqueduct structure safety, but it is unfavorable for the outer crack resistance.