As a new type of spectroscopic detection technology, Solution Cathode Glow Discharge technology is widely used to analyse and detect environmental pollutants. Although this technology has the advantages of simple structure and low cost, its sensitivity needs to be improved in detecting heavy metals. In response to the above problems, this paper built a Hydride Generation-Solution Cathode Glow Discharge spectroscopy measurement system to achieve simple and efficient detection for trace mercury (Hg) and tin (Sn) in water. In order to obtain a better detection effect, 270.64 and 253.65 nm were selected as the characteristic analysis lines of Sn and Hg in the experiment. The parameters of the excitation source are configured as the distance between electrodes of 3.5 mm, the discharge current of 60 mA, and the electrolyte flow rate of 2.12 mL·min^-1. At the same time, in the experiment, the relevant experimental conditions affecting the hydride reaction were studied, and the optimal sodium borohydride concentrations of Sn and Hg were 2% and 1.5%, the carrier gas flow rate was 141.50 and 183.95 mL·min^-1, and the pH value of the sample solution is 1.0. Subsequently, in order to further analyze the influence of coexisting ions in the water on the detection performance of the system, the experiment evaluated Pb²⁺, Ca²⁺, Zn²⁺, Cr³⁺, Cd²⁺, Na⁺, K⁺, Mn²⁺, Mg²⁺, Fe³⁺ and Cu²⁺ on the Hydride Generation-Solution Cathodic Glow Discharge technology detects the interference of Sn and Hg. The results show that only Cu²⁺ interferes significantly with detecting two elements. At the same time, Pb²⁺ interferes with detecting Hg to a certain extent, and other coexisting metal ions show no obvious interference. Based on the optimization of the above experimental conditions, the Sn and Hg calibration models were established using the standard external method under the best experimental parameters, and the detection limits of Sn and Hg were calculated to be 6.85 and 1.05 μg·L^-1. The relative standard deviations were all less than 3% (n=10). The above results indicate that the Hydride Generation-Solution Cathode Glow Discharge technology shows good analytical performance in detecting Sn and Hg. Moreover, this method has the advantages of small size, low cost, and strong anti-interference ability, and it is expected to provide a simpler and more efficient method for detecting heavy metals in water bodies.