Horizontal well external staged fracturing sand control string and method

Disclosed is a horizontal well external staged fracturing sand control string and method. A filling service string is tripped in an external staged fracturing and filling sand-control drain string. The external fracturing and filling sand-control drain string comprises a cementing external packer and a filling tool assembly connected in succession. The filling service string comprises a liquid-packing seal, a filling pipe, a filling converter, a flexible pressure tester, a rotary positioning tool, sliding sleeve opening and closing tools, and a packing sealing assembly; the filling pipe, the filling converter, the flexible pressure tester, the rotary positioning tool, the sliding sleeve opening and closing tools and the packing sealing assembly are mounted and connected onto the lower portion of the liquid-packing seal in succession; the lower end of the filling pipe and the lower end of a packing pipe are parallelly connected with the filling converter, and a liquid annulus is arranged between the filling pipe and the packing pipe. The filling tool assembly comprises an upper seal cylinder, a filling pipe external packer, and a filling sliding sleeve; the filling pipe external packer and the filling sliding sleeve are mounted and connected onto the upper seal cylinder in succession. According to the method, an open hole segment is packaged into two to ten parts; the method includes: A, tripping the filling service string in the external staged fracturing sand-control drain string; B, during filling of an upper layer, fitting a bottom packing sealing assembly and the seal cylinder to prevent filling liquid from entering a lower layer; C, repeating the step B to sequentially complete fractured gravel filling sand control for all layers.