Natural rock contains a lot of defects, such as voids, joints, and fissures, which seriously affect the mechanical properties and stability of rock mass. In this paper, the finite-discrete element method (FDEM) is used to study the mechanical properties of defected-rocks. Firstly, the uniaxial and triaxial compression tests on intact rock samples are performed to calibrate the microparameters. Then, the numerical models with different defect characteristics are established. Finally, the effects of defect content, size, shape, and orientation on mechanical behavior and energy dissipation are analyzed by uniaxial compression tests. Results indicate that the failure mode of defected-rocks is dominated by splitting. The peak strength, elastic modulus, and peak strain energy all decrease with the increase of defect content but are less affected by defect size. However, rock samples with larger size defects are more inclined to tensile failure. The peak strength and strain energy of rock samples with circular and square defects are larger than those with triangular and hexagonal defects. As the defect orientation increases, the peak strength, elastic modulus, and peak strain energy show an increasing trend. The findings in this paper have a theoretical value for studying the stability of rock mass with defects.