The electron transfer between diamond (0 0 1) surface without and with various vacancy defects and adlayer with various adsorbed atmospheric species is examined based on first-principles calculations, which plays an important role for the conductivity of diamond (0 0 1) surface. The results show that the electron transfer from the perfect diamond surface (without defect in diamond surface or subsurface layer) to the adlayer varies with the adlayer adsorbed on the surface. The largest electron transfer is about 1.08e from the perfect surface to the adlayer (10) (O2, H3O+) among the possible adlayers, such as (1) (H2O, H2O), (2) (H2O, H3O+), (3) (H2O, CO2) … (20) (N2, O2), (21) (N2, N2) layers. It is found that the vacancy defect in surface or subsurface layer also affects the diamond (0 0 1) surface conductivity by increasing or reducing the electron transfer from the surface to the adlayer. It is also noted that the electron transfer increases largely in the case that the (10) (O2, H3O+) system is adsorbed on the diamond (0 0 1) surface with vacancy defect in the surface or subsurface layer, in which the electron transfer is largest with 1.27e when the monovacancy defect forms in the subsurface layer. Our study is useful to understand the conductivity of diamond surface.