The utility model relates to a gravel packing sand retention device of a sieve tube of a horizontal well, which overcomes the defects that the prior gravel packing sand retention device of the sieve tube of the horizontal well has complicated structure and operation, and long time of field operation, and strings are needed to run for a plurality of times in the acid cleaning and back flushing operations, in the technical scheme, a sealing member (21), a bushing (3), the valve body (56) of a filling valve (5), a joint (6) and a sieve tube (8) are orderly and fixedly connected with each other from top to down; the upper end of the inner bushing (52) of the filling valve (5) is fixedly connected with the valve body (41) of an acid-washing valve, and the lower end is fixedly connected with an inner tube (7); a sealed tube (1) is installed in the inner hole of the sealing member (21); a seal ring (22) is arranged between the boss of the inner hole of the sealing body (21) and the sealed tube (1); and a gap is reserved between the sealed tube (1) above the seal ring (22) and the inner hole of the sealing member (21). The utility model has the advantages of satisfying the requirements of finishing acid-washing, gravel packing, back flushing and other operations by one completion string, and improving the working efficiency.