Abstract: The cracking of brittle materials such as rock and concrete has always been a hot and difficult issue at home and abroad, and the evolution of cracks makes it difficult to predict the mechanical behavior of brittle materials. As for the tensile, shear and tensile-shear mixed-mode cracking problem of brittle materials, a unified fracture phase-field method was presented based on spectral decomposition with the unified tensile fracture criterion in hand, and implemented in commercial finite element software by the staggered algorithm. The numerical simulation results of tensile fracture test and tensile-shear mixed-mode fracture test show that the unified fracture phase-field method is thermodynamic consistency, and can not only accurately simulate the mechanical behavior of brittle materials during crack evolution, but also accurately predict the propagation path of tensile-shear mixed-mode crack. In addition, a phase-field function was constructed by using the level-set theory to identify the interface of the phase-field crack, and the calculation formula of the phase-field crack width was deduced theoretically and then verified. This study aims to develop a phase-field method to accurately predict the tensile, shear and tensile-shear mixed-mode cracking of materials, so as to ensure the safety of civil engineering structures.