The invention discloses a combined steel pile cofferdam provided with a water swellable waterproof rubber fore shaft, which comprises cofferdam pegs and cofferdam long piles used for connecting two adjacent cofferdam pegs. Each cofferdam peg comprises a U-shaped steel sheet pile and a fore shaft sub-part, and the left and right ends of each U-shaped steel sheet pile are respectively and fixedly connected with one fore shaft sub-part. Each cofferdam long pile comprises a steel pipe pile, a fore shaft parent part arranged at the outer side of the steel pipe pile, and a water swellable rubber liner arranged in the fore shaft parent part; a tubular inner cylinder matched with each fore shaft sub-part and a notch connecting the interior of each tubular inner cylinder with the exterior of each tubular inner cylinder are arranged on the fore shaft parent part; each water swellable rubber liner is fixedly arranged on the inner wall of the corresponding tubular inner cylinder; each fore shaft sub-part is sleeved into the corresponding tubular inner cylinder; and bentonite compound filler is filled in a gap between each fore shaft sub-part and each water swellable rubber liner. By taking the combination of a rigid steel pile and a flexible steel pile to have complementary advantages, the combined steel pile cofferdam has good water resistance; the fore shaft is reliable in connection; the material of the combined steel pile cofferdam is easy to obtain; and the combined steel pile cofferdam is strong in integral structural rigidity and low in cost and is quick to construct.