The invention relates to a testing device and method for simulating flat carbonate rock reaction. The device mainly comprises a liquid storage pot, a flow meter, an acid-resistant plunger pump, a pipeline electric heating jacket, a flat clamper, a plunger metering pump, a hydraulic oil tank, a condensation tube, an acid-resistant filter, a back-pressure valve, a liquid collection pot, a pressure gauge, a molecular vacuum pump, a data acquisition and control board, and a computer. The method comprises the following steps: (1) arranging the flat rock in the inner cavity of the flat clamper, and simulating the crack width by a shim; (2) starting the plunger metering pump, applying the sealing pressure, and taking out the shim; (3) starting the molecular vacuum pump, and zero setting the pressure gauge; (4) opening the liquid storage pot accommodating acid liquor; (5) starting the computer, inputting testing parameters, and injecting the acid liquor; and (6) calculating the reaction rate of the carbonate rock at any time. The method not only can be used for accurately calculating the reaction rate of the carbonate rock, but also can analyze and evaluate major factors affecting the reaction rate of the carbonate rock; therefore, the invention provides the specific equipment and the testing method for the research on the reaction of the flat carbonate rock.