The invention discloses a control structure for automatically changing samples in a closed high-pressure reaction chamber and an automatic sample changing method. The control structure comprises a worktable lifting mechanism, a bearing plate rotating mechanism and a bearing plate positioning mechanism, wherein the worktable lifting mechanism comprises a lifting rod; a supporting seat is arranged at the top of the lifting rod; the lifting rod is connected with a driving motor; the bearing plate rotating mechanism comprises bearing plates distributed in multiple layers, a rotating shaft framework and a rotating shaft control motor; each bearing plate is arranged on the rotating shaft framework; the bearing plates can rotate around the rotating shaft framework and the rotating shaft; the rotating shaft framework is fixed together with the rotating shaft and is connected with the control motor through the rotating shaft; a plurality of round holes and one opening are distributed in each bearing plate along the external circumference; each round hole is equipped with a bearing platform for placing a sample; positioning holes corresponding to the plurality of round holes are formed along the internal circumference of each bearing plate; the bearing plate positioning mechanism comprises a first positioning rod fixed at the top of a pressure chamber and a second positioning rod fixed at the bottom of the pressure chamber. According to the control structure and the automatic sample changing method disclosed by the invention, on the premise of not interrupting and not influencing a water-rock action in the pressure chamber, rock samples are automatically changed for a single-shaft or rheological compression test.