An embodiments of the application disclose a method and a device for constructing a digital core. The method comprises the following steps: carrying out computer tomography (CT) on a core sample to obtain a three-dimensional CT grayscale image of the core sample, wherein the three-dimensional CT grayscale image comprises two-dimensional CT grayscale images corresponding to the designated areas onthe surface of the core sample; scanning the designated areas by using a scanning electron microscope to obtain two-dimensional scanning electron microscope pictures; determining porosities corresponding to the designated pixel points in the two-dimensional CT grayscale images according to the two-dimensional scanning electron microscope pictures; testing the designated areas by using an electronprobe so as to obtain mineral types corresponding to the designated pixel points in the two-dimensional CT grayscale images; determining a corresponding relation between the porosities and a grayscaledistribution range; determining porosities of pixel points in the three-dimensional CT grayscale image, and constructing the four-dimensional digital core of a target area based on the porosities ofthe pixel points in the three-dimensional CT grayscale image. After the technical scheme provided by the embodiments of the application is adopted, the accuracy of the determined digital core can be improved.