Effective tuning of carrier dynamics in two-dimensional (2D) materials is significant for multi-scene device applications. Using first-principles and ab initio nonadiabatic molecular dynamics calculations, the kinetics of O2, H2O, and N2 intercalation into 2D WSe2/WS2 van der Waals heterostructures and its effect on carrier dynamics have been comprehensively explored. It is found that the O2 molecule prefers to dissociate into atomic O atoms spontaneously after intercalation of WSe2/WS2 heterostructures, whereas H2O and N2 molecules remain intact. O2 intercalation significantly speeds up the electron separation process, while H2O intercalation largely speeds up the hole separation process. The lifetime of excited carriers can be prolonged by O2 or H2O or N2 intercalations. These intriguing phenomena can be attributed to the effect of interlayer coupling, and the underlying physical mechanism for tuning the carrier dynamics is fully discussed. Our results provide useful guidance for the experimental design of 2D heterostructures for optoelectronic applications in photocatalysts and solar energy cells.