The present disclosure provides a vent and a cap assembly of a power battery. The vent comprises a vent body and a vent body protective sheath having a wall portion and a hollow portion, the vent body is fixedly connected to a lower portion of the wall portion and sealing the hollow portion from below, an upper portion of the wall portion is fixedly connected to a cap plate for sealing a vent hole. The cap assembly of the power battery comprises a cap plate provided with a vent hole and an electrolyte-injection hole; a first electrode post connected to the cap plate; a second electrode post connected to the cap plate; and a vent fixedly provided to the vent hole; wherein the vent is the above vent.