The invention provides a horizontal double-layer buried storage tank which comprises an outer container, an inner container, an immersed pump and a drain pipe. The outer container can completely be buried underground; the inner container is arranged inside the outer container; the immersed pump is disposed at the bottom inside the inner container; and one end of the drain pipe is connected with a liquid outlet of the immersed pump and the other end of the drain pipe extends out of the outer container. According to the invention, the outer container can completely be buried underground and the immersed pump is arranged inside the inner container. Thus, the pump and the tank are integrated as a whole and the whole body is buried underground. There is no need to specially build thermal insulation facilities such as a cryogenic pump sump and the like. Therefore, a lot of manpower, material and financial resources are saved. In addition, it is guaranteed that the immersed pump is always in a low-temperature state; heat leak of the cryogenic pump sump is minimized; overall cryogenic property of the storage tank is enhanced; and daily evaporation rate of the storage tank is reduced effectively. Accordingly, it is energy saving and environmentally friendly to use the horizontal double-layer buried storage tank.