A prism for measuring liquid concentration includes: an accommodating space for accommodating a liquid; an interface formed on a bottom surface of the accommodating space; a first light transmission surface and a second light transmission surface respectively formed on two side surfaces of the accommodating space; a third light transmission surface and a light emitting surface respectively formed relative to the interface. When a first incident light beam enters the prism, the first incident light beam is reflected to the light emitting surface by the interface, and exits the prism from the light emitting surface. When a second incident light beam enters the prism to the first light transmission surface, the second incident light beam exits the prism to the accommodating space from the second incident light beam, passes through the liquid and the second light to the prism, and exits the prism from the third light transmission surface.