The invention belongs to the technical field of valves, and particularly relates to an automatic water drain valve which solves the technical problems that the design is not reasonable and the like in the prior art. The automatic drain valve comprises a main valve body with a cavity, a joint part is arranged at the lower part of the main valve, and is connected with a joint body, a valve plug assembly is arranged at the lower end of the joint body, a cavity is formed between the joint part and the joint body, an annular baffle plate which divides the cavity into a first cavity and a second cavity is arranged at the lower end surface of the joint part, an elastic piece which leans against the valve plug assembly and/or the annular baffle plate in a propping manner is arranged between the valve plug assembly and the annular baffle plate, the side part of the main valve body is provided with a first channel which communicates a box body with the first cavity, and the joint part is provided with a second channel which communicates the second cavity with the cavity. Compared with the prior art, the automatic water drain valve has the advantages that the design is reasonable, the structure is simple, the filtering effect is good, the work is reliable, the sealing effect is good, the water discharge can be regulated automatically, the maintenance personnel can maintain easily, and the maintenance cost is low.