step S1: selecting a rock sample for a CO₂ drying effect experiment, measuring a pore volume of the rock sample as V, then placing the rock sample into a weighing tray (4), vacuuming the inside of a transparent cover (8), and recording mass of the rock sample before reaction as m₁ after the rock sample is dried until the mass is stable;

step S2: taking out the rock sample in the step S1, subjecting the rock sample to the CO₂ drying effect experiment, putting the then reacted rock sample into the weighing tray (4) again, vacuuming the inside of the transparent cover (8), and then weighing wet mass m₂ of the then stably reacted rock sample;

step S3: drying the stably reacted rock sample until the mass is stable to obtain dry mass m₃ of the stably reacted rock sample;

step S4: calculating a mass difference between m₃ and m₂ as m₄, that is, the mass of evaporated water that is dried after reaction is m₄, and further calculating the volume V₀ of evaporated water that is dried after reaction, wherein

step S5: taking a solution with the volume of V₁ after reaction in the CO₂ drying effect experiment in the step S2, wherein V₁=V₀, and the mass of this solution is m₅;

step S6: placing the solution with the volume of V₁ after reaction in the step S5 on the weighing tray (4), and drying the solution under a vacuum condition until the mass of the solution is unchanged to obtain the mass m₆ of the salt crystals in this solution;

step S7: completely washing the crystals after drying the solution with the volume of V₁ obtained in the step S6 by using alcohol with the volume of V₀′ into the alcohol to obtain an alcohol mixed solution, and measuring the volume of the alcohol mixed solution as V₃, so as to obtain the volume of the crystals after drying the solution with the volume of V₁ as V₂, wherein V₂=V₃−V₀′; and

step S8: calculating a porosity error φ* occupied by the crystals after drying the solution with the volume of V₁ by using the volume V₂ of the crystals after drying the solution with the volume of V₁ obtained in the step S7 and the pore volume V of the rock sample for the CO₂ drying effect experiment, wherein the porosity error φ* occupied by the crystals after drying the solution with the volume of V₁ is the dried crystal error in the CO₂ drying experiment, the mass of the dried crystal error in the CO₂ drying experiment is m₆, and φ*=V₂/V;

wherein the apparatus for evaluating a dried crystal error in a CO₂ drying experiment comprises a heating jacket (1), a visual container (3), a weighing device (5), the transparent cover (8), a control apparatus (9), a vacuum pump (13), a damping table (14) and a heating apparatus (16), wherein the cylindrical transparent cover (8) is detachably arranged on the damping table (14), the weighing device (5) with the weighing tray (4) at the top is arranged in the transparent cover (8), the transparent visual container (3) supported by a support (6) is arranged above the weighing device (5), and the weighing tray (4) extends into the visual container (3);

a surface of the visual container (3) is provided with the heating jacket (1) that incompletely covers the surface of the visual container, the heating apparatus (16) is arranged on the damping table (14) outside the transparent cover (8), and the heating jacket (1) is connected to the heating apparatus (16);

an exhaust pipeline (7) and a vacuum pipeline (10) respectively communicated with the inside and the outside of the transparent cover (8) are arranged on the damping table (14), and the vacuum pipeline (10) can be connected to an external negative pressure source; and

the damping table (14) is further provided with the control apparatus (9), and the control apparatus (9) is electrically connected to the weighing device (5) and the heating apparatus (16).