A head-mounted display device, comprising: a body, adapted to lean against a front portion of a head of a user; two extension members (120; 120A), disposed opposite each other, wherein first ends of the two extension members (120; 120A) are respectively coupled to two opposite ends of the body and configured to rotate with respect to the body and to lean against two side portions of the head of the user; and an adjustable fixing member (140, 150, 160; 150A), coupled to each second end of the two extension members (120; 120A) and leaning against a back portion or a top portion of the head of the user, wherein the body is fixed on the head of the user through the two extension members (120; 120A) and the adjustable fixing member (140, 150, 160; 150A), and each of the two extension members (120; 120A) is adapted to contact with or depart from the two side portions of the head of the user by rotating with respect to the body; wherein the adjustable fixing member (140, 150, 160; 150A)comprises: a top side adjustable fixing member (150; 150A), adapted to contact the top portion of the head of the user, and two opposite ends of the top side adjustable fixing member (150; 150A)are respectively coupled to the second ends of the two extension members (120; 120A); and a back side adjustable fixing member, adapted to contact the back portion of the head of the user, and two opposite ends of the back side adjustable fixing member respectively coupled to the second ends of the two extension members (120; 120A), and the body is fixed on the head of the user by adjusting the top side adjustable fixing member (150; 150A) and the back side adjustable fixing member; wherein the back side adjustable fixing member further comprises an adjusting mechanism and two adjusting belts positioned between the head of the user and an outside portion of the back side adjustable fixing member, the adjusting belts respectively connecting the adjusting mechanism with the second ends of the corresponding extension members (120; 120A). a body, adapted to lean against a front portion of a head of a user; two extension members (120; 120A), disposed opposite each other, wherein first ends of the two extension members (120; 120A) are respectively coupled to two opposite ends of the body and configured to rotate with respect to the body and to lean against two side portions of the head of the user; and an adjustable fixing member (140, 150, 160; 150A), coupled to each second end of the two extension members (120; 120A) and leaning against a back portion or a top portion of the head of the user, wherein the body is fixed on the head of the user through the two extension members (120; 120A) and the adjustable fixing member (140, 150, 160; 150A), and each of the two extension members (120; 120A) is adapted to contact with or depart from the two side portions of the head of the user by rotating with respect to the body; wherein the adjustable fixing member (140, 150, 160; 150A)comprises: a top side adjustable fixing member (150; 150A), adapted to contact the top portion of the head of the user, and two opposite ends of the top side adjustable fixing member (150; 150A)are respectively coupled to the second ends of the two extension members (120; 120A); and a back side adjustable fixing member, adapted to contact the back portion of the head of the user, and two opposite ends of the back side adjustable fixing member respectively coupled to the second ends of the two extension members (120; 120A), and the body is fixed on the head of the user by adjusting the top side adjustable fixing member (150; 150A) and the back side adjustable fixing member; wherein the back side adjustable fixing member further comprises an adjusting mechanism and two adjusting belts positioned between the head of the user and an outside portion of the back side adjustable fixing member, the adjusting belts respectively connecting the adjusting mechanism with the second ends of the corresponding extension members (120; 120A). a top side adjustable fixing member (150; 150A), adapted to contact the top portion of the head of the user, and two opposite ends of the top side adjustable fixing member (150; 150A)are respectively coupled to the second ends of the two extension members (120; 120A); and a back side adjustable fixing member, adapted to contact the back portion of the head of the user, and two opposite ends of the back side adjustable fixing member respectively coupled to the second ends of the two extension members (120; 120A), and the body is fixed on the head of the user by adjusting the top side adjustable fixing member (150; 150A) and the back side adjustable fixing member; wherein the back side adjustable fixing member further comprises an adjusting mechanism and two adjusting belts positioned between the head of the user and an outside portion of the back side adjustable fixing member, the adjusting belts respectively connecting the adjusting mechanism with the second ends of the corresponding extension members (120; 120A).