The invention discloses a stretching device for rubber swelling property testing and a testing method. The stretching device comprises a frame, a movable plate arranged in the frame, and a rotating mechanism for driving the movable plate to move back and forth. A first clamping mechanism and a second clamping mechanism for clamping the two ends of rubber respectively are correspondingly arranged on the frame and the movable plate. By means of the structure, the position of the movable plate is regulated through the rotating mechanism, and then the distance between the first clamping mechanism and the second clamping mechanism is adjusted to obtain the stretching amount and deformation amount needed by the rubber. Due to the fact that the frame is adopted for restraining the movement locus of the movable plate, the movement stability and reliability of the movable plate are guaranteed, and the reliability of rubber swelling testing data is ensured.