A high-temperature in-situ loaded computed tomography (CT) testing system based on a laboratory X-ray source and a method therefor are provided. A dynamic sealing device is adopted. A pull-up pressure rod and a pull-down pressure rod are allowed to rotate circumferentially and move axially. Meanwhile, a high-temperature furnace is fixed without rotating or moving, such that the high-temperature furnace is flat in an imaging direction to shorten an imaging distance and improve imaging quality. An independent tensile testing machine is utilized to achieve high-load loading. The in-situ measurement of internal deformation and damage information of a specimen under tensile or compressive load in a high-temperature environment is implemented. By taking advantage of the miniaturization design of the high-temperature device, the accuracy of the damage test using the laboratory X-ray source is increased. Tests and researches on the internal damage and failure behavior of the high-temperature materials can be conducted.