Due to illegal emission of waste water by the industrial and chemical enterprises, the soil and water resources around the contaminated sites are polluted. It is very important to define the polluted depth of groundwater in the later investigation and evaluation of contaminated sites, because the polluted depth of groundwater is the main basis of health risk assessment of groundwater. Take the case of environmental investigation of a chemical plant contaminated site in Hebei, the cone type water-stopping devices were used with 2 layers setting for effective stratified water shut-off, in order to obtain the accurate definition of the polluted depth of groundwater. This paper elaborates the technical methods by stratified water shut-off device in the investigation and definition of the polluted depth of Quaternary groundwater. The practice proves that this technology has advantages of simple construction and flexible use with good sealing effect and the technology is effective and feasible.