The utility model discloses a horizontally opened top-hung window, and relates to the technical field of windows and doors. The horizontally opened top-hung window comprises a window frame and a glass window, wherein the glass window is arranged on the window frame; a one-way rotation stop mechanism is arranged between the upper frame of the glass window and the upper frame of the window frame; another one-way rotation stop mechanism is arranged between the lower frame of the glass window and the lower frame of the window frame; a connecting line of the two one-way rotation stop mechanisms is overlapped with a central line in the vertical direction of the glass window; symmetrical handles are arranged on the left side and the right side of the window frame. Each one-way rotation stop mechanism comprises a rotary shaft fixed to the glass window and a rotation stop sleeve fixed to the window frame, the rotary shaft sleeve is connected with the interior of the rotation stop sleeve in a sleeving way; semi-moon shaped movable teeth are arranged in the rotation stop sleeve; fixed teeth are arranged on the rotary shaft; the fixed teeth are matched with the movable teeth so as to enable the glass window to rotate only in one direction under the push action of external force, and the glass window can keep a fixed state without the effect of the external force. When the horizontally opened top-hung window is used, the glass window can be pushed only to rotate around the rotary shaft and can be folded, and can achieve rotation and self-locking only via the one-way rotation stop mechanisms.