Malodor issues, in particular, hydrogen sulfide and volatile organic compounds in drainage systems in have been bothering Hong Kong residents for decades. These pollutants are colorless but have an unbearable smell with a low odor threshold, which means people can easily detect the odor. This continuous study reports the removal of hydrogen sulfide by innovative multi-functional hydrogel in both coastal areas and urban drainage systems in Tsuen Wan and Hung Hom provided by the Drainage Service Department of HKSAR and additionally computed the effective distance of hydrogel. The 70%-95% reduction was observed in Tsuen Wan and Hung Hom promenades, and active ingredients could be carried by streamflow for up to 650m to treat the polluted stormwater downstream. However, some minor stench still existed was predicted to be VOCs. Further analysis shows that some stinky volatile organic compounds with low odor threshold were identified in Tsuen Wan coastal area and Kai Tak River, including terpenes, aromatic hydrocarbons, fatty acids, and organosulfur leading to earthy, pungent, and sharp smell on sampling sites. In addition, two different H2S dispersion models were built to simulate box culvert and manhole drainage systems in Hong Kong. The results illustrate that the H2S detection area could be suppressed to the level that people can avoid stinky smell after treatment with hydrogel.