An upper cover assembly suitable for an atomizing device of an electronic cigarette, comprising an upper cover, a liquid filling cap movable relative to the upper cover between a usage position and a liquid filling position, and a mouthpiece, wherein the upper cover is sequentially provided with a liquid filling hole and a smoke outlet hole along the path of the liquid filling cap moving from the usage position to the liquid filling position, the liquid filling cap is provided with a through hole, the mouthpiece is integrally formed with the liquid filling cap on a surface of the liquid filling cap away from the upper cover and is in communication with the through hole; when the liquid filling cap is in the usage position, the liquid filling cap covers the liquid filling hole and the through hole is in communication with the smoke outlet hole; when the liquid filling cap is moved from the usage position to the liquid filling position, the liquid filling cap is displaced from the liquid filling hole and the liquid filling hole is opened; the upper cover is provided with a sliding groove having an opening formed at one end thereof on both sides of the moving direction of the liquid filling cap, the liquid filling hole and the smoke outlet hole are sequentially provided between the two sliding grooves along the path of the liquid filling cap moving from the usage position to the liquid filling position, the liquid filling cap is slidably mounted in the sliding grooves through the openings; the liquid filling cap comprises a cover body and two flanges extending outward from side edges of both sides of the cover body, and the two flanges are slidably engaged in the two sliding grooves; one end of the upper cover away from the opening is provided with a receiving groove, the receiving groove connects two ends of the two sliding grooves away from the opening, the liquid filling cap includes a limiting edge formed by extending outward from a lower edge of the cover body, the limiting edge is located between the two flanges and is able to move into or out from the receiving groove, the limiting edge is received in the receiving groove and the cover body abuts against an inner wall of the receiving groove when the liquid filling cap is in the usage position; characterized in that the upper cover comprises a bottom cover and a pressing cover disposed above the bottom cover, the liquid filling hole and the smoke outlet hole are sequentially provided in the bottom cover along the path of the liquid filling cap moving from the usage position to the liquid filling position, the pressing cover is recessed inwardly from an edge away from the liquid filling hole to form a notch, the smoke outlet hole and the liquid filling hole are both received and exposed in the notch; a surface of the pressing cover facing the bottom cover is formed with two first recesses surrounding the notch and a second recess connected between the two first recesses, when the pressing cover is mounted on the bottom cover, the two first recesses and the second recess are enclosed by the bottom cover to form the two sliding grooves and the receiving groove. the upper cover is provided with a sliding groove having an opening formed at one end thereof on both sides of the moving direction of the liquid filling cap, the liquid filling hole and the smoke outlet hole are sequentially provided between the two sliding grooves along the path of the liquid filling cap moving from the usage position to the liquid filling position, the liquid filling cap is slidably mounted in the sliding grooves through the openings; the liquid filling cap comprises a cover body and two flanges extending outward from side edges of both sides of the cover body, and the two flanges are slidably engaged in the two sliding grooves; one end of the upper cover away from the opening is provided with a receiving groove, the receiving groove connects two ends of the two sliding grooves away from the opening, the liquid filling cap includes a limiting edge formed by extending outward from a lower edge of the cover body, the limiting edge is located between the two flanges and is able to move into or out from the receiving groove, the limiting edge is received in the receiving groove and the cover body abuts against an inner wall of the receiving groove when the liquid filling cap is in the usage position; characterized in that the upper cover comprises a bottom cover and a pressing cover disposed above the bottom cover, the liquid filling hole and the smoke outlet hole are sequentially provided in the bottom cover along the path of the liquid filling cap moving from the usage position to the liquid filling position, the pressing cover is recessed inwardly from an edge away from the liquid filling hole to form a notch, the smoke outlet hole and the liquid filling hole are both received and exposed in the notch; a surface of the pressing cover facing the bottom cover is formed with two first recesses surrounding the notch and a second recess connected between the two first recesses, when the pressing cover is mounted on the bottom cover, the two first recesses and the second recess are enclosed by the bottom cover to form the two sliding grooves and the receiving groove.