In this paper, we propose to build a system of classical field equations compatible with general relativity by constructing a discrete space-time scalar field. The theory interprets dark energy as the space-time lattice potential V(φ), and dark matter as the scalar field kinetic energy (including space-time gradient term) and matter coupling effect, and realizes the unified description of the two. And the physical prediction consistent with the data of Planck satellite and supernova is given, and through the power spectrum analysis and observation comparison, the theoretical phase frame matches with the experimental data within the error range, which provides a new direction for the cross-study of spacetime discretization and cosmology.