The invention discloses a method for producing low-alloy peritectic steel by a conventional slab continuous casting machine. The method comprises the technological processes of decarburization converter smelting, LF refining and slab continuous casting. Through the adjustment on the continuous casting procedures of the conventional slab continuous casting machine, the phenomenon of large liquid level fluctuation during peritectic steel pouring is eliminated, the shock mark depth of a casting blank is obviously reduced, cracks and concave parts in the surface of the casting blank are eliminated, the conventional slab continuous casting machine can produce flawless low-alloy peritectic steel in batches, and high-quality raw materials are provided for low-alloy high-strength steel stable in production performance.