A non-destructive method for evaluating a structure of a water-absorbent resin through X-ray computer tomography, the method comprising: a step 1 of placing the water-absorbent resin to be evaluated on a sample stage of an X-ray computer tomography apparatus; a step 2 of performing X-ray computer tomography on the water-absorbent resin by using the X-ray computer tomography apparatus to acquire tomographic image data of the water-absorbent resin; a step 3 of analyzing the tomographic image data by using image analysis software to obtain a cross-sectional image of the water-absorbent resin; characterised in that it further comprises: either a step 4a of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a total cross-sectional area of cavity portions in the water-absorbent resin from the cross-sectional image of the water-absorbent resin; or a step 4b-1 of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a cross-sectional area of a cross section of the water-absorbent resin in which cavities are filled from the cross-sectional image of the water-absorbent resin, in combination with a step 4b-2 of subtracting the total cross-sectional area from the cross-sectional area to calculate the total cross-sectional area of cavity portions in the water-absorbent resin; and a step 5 of calculating a cavity area ratio of the water-absorbent resin by Equation: cavity area ratio % = { total cross-sectional area B of cavity portions in the water-absorbent resin / total cross-sectional area A of resin portions in the water − absorbent resin total cross-sectional area B of cavity portions in the water − absorbent resin × 100. a step 1 of placing the water-absorbent resin to be evaluated on a sample stage of an X-ray computer tomography apparatus; a step 2 of performing X-ray computer tomography on the water-absorbent resin by using the X-ray computer tomography apparatus to acquire tomographic image data of the water-absorbent resin; a step 3 of analyzing the tomographic image data by using image analysis software to obtain a cross-sectional image of the water-absorbent resin; characterised in that it further comprises: either a step 4a of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a total cross-sectional area of cavity portions in the water-absorbent resin from the cross-sectional image of the water-absorbent resin; or a step 4b-1 of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a cross-sectional area of a cross section of the water-absorbent resin in which cavities are filled from the cross-sectional image of the water-absorbent resin, in combination with a step 4b-2 of subtracting the total cross-sectional area from the cross-sectional area to calculate the total cross-sectional area of cavity portions in the water-absorbent resin; and a step 5 of calculating a cavity area ratio of the water-absorbent resin by Equation: cavity area ratio % = { total cross-sectional area B of cavity portions in the water-absorbent resin / total cross-sectional area A of resin portions in the water − absorbent resin total cross-sectional area B of cavity portions in the water − absorbent resin × 100. either a step 4a of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a total cross-sectional area of cavity portions in the water-absorbent resin from the cross-sectional image of the water-absorbent resin; or a step 4b-1 of, by using image processing software, measuring a total cross-sectional area of resin portions in the water-absorbent resin and a cross-sectional area of a cross section of the water-absorbent resin in which cavities are filled from the cross-sectional image of the water-absorbent resin, in combination with a step 4b-2 of subtracting the total cross-sectional area from the cross-sectional area to calculate the total cross-sectional area of cavity portions in the water-absorbent resin; and a step 5 of calculating a cavity area ratio of the water-absorbent resin by Equation: cavity area ratio % = { total cross-sectional area B of cavity portions in the water-absorbent resin / total cross-sectional area A of resin portions in the water − absorbent resin total cross-sectional area B of cavity portions in the water − absorbent resin × 100.