The non-point source pollution is not easy to be controlled, and it is one of the important environmental problems facing the world. Taking Hohhot, a typical city in the arid semi-arid region in China, as an example, four monitoring sites in the city were selected, water samples from six rainfall events were collected, and pollutants such as heavy metals, ammonia, nitrate nitrogen, phosphorus and suspended matter were examined, and the water quality of the rain runoff was comprehensively evaluated by the principal component analysis and the correlation analysis. The results showed that the total phosphorus contents of monitoring points in the street were the largest and those of monitoring points in gas stations were the smallest in rainfall runoff. Arsenic, cobalt, and chromium were less than the Class I standard for environmental quality standards for surface water according to Chinese standard (GB 3838-2002). Concentrations of cadmium, copper, and iron were greatest in street monitoring sites, while nickel, lead, and zinc were greatest in roof monitoring sites, and manganese was greatest in car park monitoring sites. There was minimal contamination at gas station monitoring sites and the greatest contamination at street monitoring sites. Heavy metals and phosphorus were the main contributing factors to pollution at street monitoring sites, while the main contributing factors at gas station monitoring sites were total suspended substances.