The water spider (Argyroneta aquatica), is currently the world's only species inhabiting in water of streams, ponds, swamps and other water bodies and preying on small fishes, shrimps and insect larvae. It can be widely found in Palearctic area, including Europe and North of Asia. This paper observes the structure of tracheal systems in the water spider, and compared it with three common terrestrial spiders, Arctosa ningboensis, Psechrus senoculatus and Araneus ventricosus. The trachea system of water spiders were found in the form of two cylinders, with many tiny tubes (tracheal) extending forwardly into the cephalothorax and backwardly into the mid and posterior parts of abdomen from the ends of the cylinders. Tracheal structures in others are constructed in four simple tubes. The complex structure of the water spider's tracheal systems has revealed a higher usage of the tracheal system, and indicates the water spider's metabolism and exercise level also exceeds the common terrestrial spiders. This paper not only observed and compared the water spider tracheal systems, but also discussed the relationship between the structure and function of the system. It revealed that highly complex tracheal system is an adaptation to the unique underwater environment, proved the importance of the tracheal system in spider evolution, and filled the blank of Chinese spider tracheal system study.