Abstract: In order to analyze the influence of the low flow velocity of water on the leaching characteristics of cement-based materials like cement mortar in a short time, 1 mol/L NH₄Cl solution with the flow velocity of 0, 0.5, 1.0 and 2.5 m/s was used as corrosion solutions to carry out accelerated leaching experiments on the cement mortar cylinder specimens with the water-cement ratio of 0.45 at room temperature(25 ℃). By using some measurements, such as the phenolphthalein indicator, saturation-drying weighing, X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectrometer (SEM/EDS), the leaching depth, porosity, phase composition and microstructure morphology of specimens before and after leaching for 15, 30 and 60 days were analyzed. Results show that the leaching depth and porosity of specimens increase with the leaching time and flow velocity. During the immersion (the flow velocity is zero), the leaching depth of specimens is linear with the square root of the leaching time. With the increase of flow velocity, there appear gradually a non-linear relationship between the leaching depth of specimen and the square root of leaching time, and a decrease in the relative intensity of the diffraction peaks of the CSH phase in the powder sample from the leaching zone of specimen, and an accelerated the dissolution of calcium hydroxide and CSH gel in cement mortar, which indicates that the flow velocity can accelerate the microstructure deterioration of cement mortar in the flowing solution.