Altered igneous reservoirs have low porosity and permeability, compact structure and certain heterogeneity. A simple digital core with certain generality and multi-parameter constraints can be constructed to characterize the microscopic pore structure and mineral composition. In this paper, based on core X-ray, CT images and whole-rock mineral analysis, threshold segmentation of mass content and grayscale distribution of various minerals in different lithologies of igneous rocks in the buried hill of Huizhou depression is carried out to construct digital core of altered igneous rocks. The results show that after converting the mineral mass content into volume content, the minerals of altered igneous rocks in Huizhou depression can be classified into components. According to the range of grayscale value, components can be divided into six parts. Due to the difference of the content of components in different lithologies of igneous rocks, differentiated grayscale threshold segmentation is needed to obtain the digital core for a single lithology. The final digital core generation process includes two steps: building a single component digital core, and stacking and combining. This kind of universal digital core model can support the subsequent pore scale numerical simulation and comprehensive rock physics research.