An anti-overflow catheter assembly for an indwelling needle comprises a flexible catheter (1), a catheter seat (2) connected with one end of the catheter (1), and a sealing needleless adaptor (3). The sealing needleless adaptor (3) comprises a sealing base (32) and a sealing element (31). One end of the sealing base (32) is installed at the outer end of the catheter seat (2). The sealing element (31) is a soft elastic component, and integrally consists of an upper sealing sheet (311), a lower sealing sheet (313) and a middle sealing section (312). A centrally-located closing slit (314) is provided on the end face of the upper sealing sheet (311). The slit (314) passes from the upper sealing sheet (311), through the middle sealing section (312), and into the lower sealing sheet (313). The length of the slit (314) is longer than the radius of the upper sealing sheet (311). The sealing base (32) has a cylindrical inner cavity running through from left to right, in which the sealing element (31) is installed. The upper sealing sheet (311) and the lower sealing sheet (313) are hermetically secured on the two longitudinal end faces of the inner cavity of the sealing base (32) respectively, and there is a redundant space between the middle sealing section (312) and the cylindrical inner cavity. The whole needleless adaptor has a simple structure and a small quantity of components, and thus has a low cost.La présente invention concerne un ensemble cathéter anti-reflux pour une aiguille à demeure qui comprend un cathéter flexible (1), une embase de cathéter (2) connectée à une extrémité du cathéter (1), et un adaptateur détanchéité sans aiguille (3). Ladaptateur détanchéité sans aiguille (3) comprend une base détanchéité (32) et un élément détanchéité (31). Une extrémité de la base détanchéité (32) est installée au niveau de lextrémité extérieure de lembase de cathéter (2). Lélément détanchéité (31) est un composant élastique souple, et entièrement constitué dune feuille dét
