The invention discloses a well completion method for a glass fiber reinforced plastic sieve tube of a coal bed gas horizontal well, which is characterized in that the glass fiber reinforced plastic sieve tube is adopted for carrying out well completion, a washing tube is inserted in the glass fiber reinforced plastic sieve tube, hydraulic action is applied to the stacked pulverized coal blocking a horizontal well section at the end of the glass fiber reinforced plastic sieve tube by assistance of the washing tube, and the annular space between tubular columns is separated and sealed by matching of a sealed chamber and a sealed tube so as to increase the hydraulic action effect, so that the glass fiber reinforced plastic sieve tube can be smoothly inserted, the insertion of the glass fiber reinforced plastic sieve tube in a horizontal well with a large ratio of horizontal length to vertical depth can be applicable, coal bed wall support is improved while a channel for subsequent coal bed gas reforming is provided, gel breaking and hydraulic cleaning for any well section of a coal bed can also be realized through the washing tube during well completion operation, wall cakes can be eliminated in time, the coal bed is protected, and the pollution is avoided.