Packing device for cased hole gravel packing of horizontal well

A packing device for cased hole gravel packing of a horizontal well comprises a cased packing service tool and a cased packing tool, wherein a plurality of first packing holes are formed at the upper edge of the cased packing service tool circumferentially; the cased packing service tool is connected in the cased packing tool; the cased packing tool comprises an upper connector, a packing switch assembly, an outer sleeve, a locating ring and a lower connector; the upper connector and the lower connector are connected with the left end and the right end of the cased packing tool respectively; the left end of the packing switch assembly is connected with the upper connector; the right end of the packing switch assembly is connected with the outer sleeve; the lower connector is connected with the right end of the outer sleeve; the locating ring is connected with the outer sleeve and located on the left side of the lower connector; the packing switch assembly comprises a packing cylinder, a sliding sleeve and a p