Abstract: 1,4-dioxane is toxic, easily entering the ecological system to cause damage of the environment and people health. It is relatively strong affinity for water, and not easy to be biodegradable in the natural environment. 1,4-dioxane is a new type of organic contaminants in groundwater, has been defined as one of the controlled substances by World Health Organization (WTO). But only few countries defined the limited value of 1,4-dioxane content in groundwater, as Japan is 50 μg/L. In China, this research field is rarely concerned, and there is none report for detection method of 1,4-dioxane in groundwater either. Purge and Trap-Gas Chromatography/Mass Spectrometry(P&T-GC/MS) is a fast, simple analytical method with low detection limit, in recent years it has been widely used in water analysis. This paper chooses P&T-GC/MS for the determination of trace 1,4-dioxane in groundwater. In the experiment, ammonium sulfate was added as sample protective agent to increase the sample storage time and prevent the deterioration from microbial degradation and other factors, but also improve the efficiency of the purge desorption for 1,4-dioxane, the instrument response value increased by one times. Under the optimized operating conditions of the instrument, the precision is 5.9%-6.6%; the detection limit is 1.02 μg/L, has been reached WHO standard for drinking water quality limit (0.05 mg/L), and is lower than the isotope dilution-GC-MS detection limit of 3.2 μg/L. This method can meet the demands during geological investigation and environmental assessment.