The invention discloses a separate-layer fracturing sand control string for a thermal production well and a sand control method thereof, and belongs to the technical field of the sand control in oilfield development. The string comprises two layers of strings of a sand control outer pipe and a process inner pipe, wherein the sand control outer pipe comprises a top packer, a backwashing device, a fracturing sealing tool, a fracturing filling outer tool, a one-way sealing tool, a screen pipe, an outer locating device, an interlayer packer and a pipe plug; the process inner pipe comprises a releasing tool, a fracturing filling device, a sliding sleeve switch, a locating tool and a fracturing filling conversion device. The sand control method comprises the following sand control steps of setting the top packer; releasing; setting the interlayer packer; lowering the process inner pipe, and carrying out fracturing sand control filling construction on a lower perforation interval; opening a circulating passage, and carrying out circulating filling; backwashing a well; lifting the processing inner pipe, and carrying out fracturing filling construction and circulating filling construction on other perforation intervals. As tools such as the backwashing device and the fracturing filling conversion device are used, the separate-layer fracturing sand control string for the thermal production well and the sand control method thereof have the advantages of well backwashing without moving the string, fracturing without casing pressure, flow-back prevention and the like.