Hydraulic system is the core driving power of hydraulic support, and its performance directly affects the use of hydraulic support. The content of chloride ion in hydraulic transmission medium is one of the important reasons for the working failure of hydraulic support. Nowadays our country mainly uses the simply treated mine water as fluid in the hydraulic support system. In order to ensure hydraulic support can work safely and reliably underground, this study selected two representative kinds of mine fields in Huainan coal mine area, focusing on the analysis of the various factors which influence the introduction of chloride ion in the transmission medium of hydraulic support, and exploring the solution. The experimental results showed that different crude mine water and different water treatment processes were the main factors of introducing chloride ion. The study has important guiding significance of safely using Electro-hydraulic Control System in hydraulic support and achieving high productivity and high efficiency of the fully mechanized working face.