The invention provides a large-size load test apparatus. The apparatus sequentially comprises, from top to bottom, a first pressure applying device (1), a hydraulic jack (2), a force testing sensor (3), a second pressure applying device (4) and a test platform (5). The invention also provides a method of using the apparatus. The method includes the following steps: installing the first pressure applying device (1), the force testing sensor (3), the hydraulic jack (2), the second pressure applying device (4), a workpiece (6) and the test platform (5), driving the hydraulic jack (2) to apply pressure, monitoring load reading numbers of the force testing sensor (3), stopping pressing, carrying out pressure maintaining, and releasing pressure by the hydraulic jack (2) after pressure maintaining ends. The load test apparatus is highly universal, and enables a load test to be carried out in a safe, effective and controllable manner to guarantee that products meet manufacturing requirements.