A chuck structure includes: a first chuck, provided with a seat slidable relatively thereto, the seat provided with a first stop; a limiting element, swingable relatively to the seat, and provided with a second chuck; and an operating element, respectively connected with the limiting element and a second chuck, and driving the second chuck to move relatively to the first chuck to form an accommodation space between the first chuck and second chuck, an elastic element configured between the operating element and limiting element, and the elastic element pressing against the limiting element to approach the seat, allowing the second and first stops to be in contact with each other. The present invention can use the operating element 3 to adjust the size of the accommodation space, and the second stop in contact with first stop to make the operating element can only be rotated in a single direction.