The invention discloses a one-off forming mold of a double-layer rubber tube. The forming mold comprises a first mold core, a second mold core and a mold sleeve. The first mold core sleeves the second mold core. The second mold core sleeves the mold sleeve. The first mold core comprises a round bulge, a ring sleeve, a first mold core body, a cone-shaped connecting part and a second mold core body. The round bulge is located in the middle of the ring sleeve. One end of the first mold core body is connected to the round bulge, and the other end of the first mold core body is connected to one end of the cone-shaped connecting part. The second mold core body is connected to the other end of the cone-shaped connecting part. The second mold core comprises thread, an annular bulge, a cone-shaped outlet, round holes, a through hole and grooves, wherein the thread is close to the first mold core, the annular bulge is located below the thread, the cone-shaped outlet is formed below the annular bulge, the round holes are irregularly formed in the annular bulge, and the through hole is formed in the cone-shaped outlet. The one-off forming mold increases the forming speed, reduces the cost and increases the production efficiency.