Defect engineering of two-dimensional (2D) materials is an important approach to control the performance and achieve desired functions for the related devices. In this paper, the influence of various types of vacancy defects on the electronic and optical properties of graphene/ molybdenum disulfide (MoS₂) heterostructures was studied by a first principles method based on density functional theory. The existence of vacancy defects in a single layer, and in both layers were investigated, respectively. Besides, the influence of vacancy density was considered as well. The evolutions of electrical band structure and differential charge density difference were revealed regarding different vacancy types. And the evolutions of optical absorption coefficient (α(ω)), optical refractive index (n(ω)), and optical energy loss spectrum (L(ω)) were discussed in detail. This study could provide important information for the application of defect engineering in the 2D heterostructures-based devices.