The invention discloses a four-way casing quick-mounting structure applied to an oil well. The four-way casing quick-mounting structure comprises a casing main body and a limiting mechanism, the casing main body comprises a first casing, a second casing and a connecting pipe, the diameter of the second casing is larger than that of the first casing, the first casing is connected with the second casing through a connecting mechanism, the connecting pipe is fixedly connected with the end, close to the first casing, of the second casing, the first casing is sleeved with the connecting pipe, the limiting mechanism comprises limiting openings, limiting blocks, mounting blocks and springs, the two limiting openings are formed in the two opposite ends of the connecting pipe, mounting grooves areformed in the two mounting blocks, the two ends of the springs are fixedly connected with the bottoms of the mounting grooves and the bottoms of the limiting blocks correspondingly, and the limiting blocks are matched with the limiting openings and the mounting grooves in size and shape. By means of the connecting mode of the structure, the mounting and dismounting processes are simple and convenient, operation is easy, and constructors can complete mounting and dismounting with bare hands.