The invention discloses a hot-cast anchor stay rope horizontal casting tool and a casting method. The tool comprises a positioning mold and a casting mold; the positioning mold is arranged at a small cone end of a casting anchor tool; the casting anchor tool is fixed with a rope body; the casting mold is communicated with an anchor cavity of the casting anchor tool; and a sprue and a riser are arranged on the casting mold, and are respectively communicated with the anchor cavity of the casting anchor tool through different pipelines. The hot-cast anchor stay rope horizontal casting tool and the casting method have no need to manufacture the casting mold whose inner cavity has the same size with the anchor cavity of the anchor tool, and are short in production period and low in cost; the casting mold is provided with the sprue and the riser for facilitating air exhausting to guarantee the alloy casting rate so as to guarantee the casting quality; the positioning mold guarantees the coaxiality and the verticality of the rope body and the anchor tool, and guarantees the casting position accuracy to improve the rope length precision; a molten alloy is directly cast in the casting anchor tool; and a cone is totally matched with the anchor cavity, so that the casting body shrinkage value is reduced, and the rope length precision is improved.