The main component of Wang Xi capsule is nano-selenium. Chemically speaking, nano-selenium is a reduced selenium, which is equivalent to zero-valent selenium. Zero-valent selenium has no physiological function, and will not be absorbed and utilized after entering the human body, but will be excreted intact. As a new product prepared by nanotechnology, nano-selenium can not only be absorbed and utilized by human body, but also play the unique functions of organic selenium and inorganic selenium, such as antioxidation and immune regulation. Most importantly, it has low toxicity that inorganic selenium and organic selenium do not have, and is a unique selenium product in the world.