The invention provides a method for quick locating and stable construction of a double-wall steel cofferdam of a torrential rock riverbed. The problems that in a torrential rock riverbed environment,a double-wall steel cofferdam is difficult to locate accurately under the effect of water current force when lowered, and the double-wall steel cofferdam is difficult to stabilize because no coveringlayer is on the riverbed after being lowered are solved. As shown from figure 1 to figure 5, according to the method, a percussion drill is utilized firstly so that locating holes are constructed; andthen locating piles are lowered according to positions of designed locating holes. Concrete is poured into the piles after the locating piles are lowered in order to guarantee that the locating pilesare anchored firmly in the locating holes. Displacement of the cofferdam is restrained through the locating piles when the steel cofferdam is lowered. After the double-wall steel cofferdam is loweredto the riverbed, between-wall concrete is poured between the double walls of the double-wall steel cofferdam according to a designed height; the double-wall steel cofferdam and the locating piles arebonded into a whole; and thus the purpose of stabilizing the double-wall steel cofferdam is achieved.