Water-sewage diversion of tunnel construction drainage is an important engineering technique to reduce tunnel construction sewage discharge. However, the leaching substances of unstable tunnel shotcrete can affect the drainage water quality. Therefore, the study of the influence of leaching substances on the water quality during the stabilization process of shotcrete is of great significance for the precise implementation of wastewater separation technology. The static and dynamic experimental methods have been applied to the systematic study of the pollution indicators and leaching laws of shotcrete. The static experimental results show that when water comes into contact with newly poured concrete, the large release of alkaline substances can lead to a rapid increase in the pH of the water, becoming an important pollution factor affecting the water quality. The dynamic experimental results show that the curing time of concrete, the ratio of water to concrete (the volume-to-volume ratio of water sample to concrete， L/S), and the contact area between concrete and water all affect the water quality. When the curing time of the concrete is less than three days, the calcium hydroxide crystal inside the concrete is not solidified by the C-S-H gel, which is easy to continue to precipitate, leading to the pH of the contact water sample exceeding the standard. With the increase of curing time, the leaching alkaline substances decrease significantly. When the maintenance time reaches 28 days, the pH of the leaching solution drops below 9, which can meet the requirements of comprehensive wastewater discharge. When the L/S ratio is low, the leaching substance has a significant impact on the pH and alkalinity of the water sample. When the L/S ratio exceeds 40∶1, the leaching substance has no significant impact on the water quality of the water sample. The larger the contact area between the concrete and water samples, the easier it is for alkalis in the concrete to dissolve and precipitate, and the more significant the impact on the pH and alkalinity of the water quality.