An indoor unit of a wall-mounted air conditioner comprising: a chassis ; a screen assembly ; and a cleaning assembly disposed at one end of the screen assembly and connected with the screen assembly by a fastening structure, wherein the fastening structure is a detachable structure, that comprises a first threaded structure; wherein the cleaning assembly is mounted on the chassis , or the screen assembly is mounted on the chassis , or the cleaning assembly and the screen assembly are both mounted on the chassis ; wherein the screen assembly comprises a grille assembly , and wherein the cleaning assembly comprises a cleaning box disposed below the grille assembly and comprising a third connecting member extending upwardly from an edge of an opening of the cleaning box , and wherein the first threaded structure comprises a first locking screw penetrating the third connecting member and threaded with one end of the grille assembly ; wherein the chassis comprises: a bottom wall defining an accommodating space ; and a rear side wall connected to a rear side of the bottom wall , wherein a lower portion of the cleaning assembly is mounted in the accommodating space ; wherein an upper portion of the cleaning assembly is connected with the rear side wall by a second threaded structure, the cleaning assembly comprises a fourth connecting member protruded from the cleaning box and extended away from the other end of the screen assembly ; and wherein the second threaded structure comprises a second locking screw penetrating the fourth connecting member and threaded with the rear side wall ; and wherein the fourth connecting member is integrally formed on a rear side edge of the third connecting member . a chassis ; a screen assembly ; and a cleaning assembly disposed at one end of the screen assembly and connected with the screen assembly by a fastening structure, wherein the fastening structure is a detachable structure, that comprises a first threaded structure; wherein the cleaning assembly is mounted on the chassis , or the screen assembly is mounted on the chassis , or the cleaning assembly and the screen assembly are both mounted on the chassis ; wherein the screen assembly comprises a grille assembly , and wherein the cleaning assembly comprises a cleaning box disposed below the grille assembly and comprising a third connecting member extending upwardly from an edge of an opening of the cleaning box , and wherein the first threaded structure comprises a first locking screw penetrating the third connecting member and threaded with one end of the grille assembly ; wherein the chassis comprises: a bottom wall defining an accommodating space ; and a rear side wall connected to a rear side of the bottom wall , a bottom wall defining an accommodating space ; and a rear side wall connected to a rear side of the bottom wall , wherein a lower portion of the cleaning assembly is mounted in the accommodating space ; wherein an upper portion of the cleaning assembly is connected with the rear side wall by a second threaded structure, the cleaning assembly comprises a fourth connecting member protruded from the cleaning box and extended away from the other end of the screen assembly ; and wherein the second threaded structure comprises a second locking screw penetrating the fourth connecting member and threaded with the rear side wall ; and wherein the fourth connecting member is integrally formed on a rear side edge of the third connecting member . <EOS>