Based on the aerothermodynamic principles, a kind of breathing biocover system was designed to enhance O2 supply efficiency and methane (CH4) oxidation capacity. The research showed that O2 concentration (v/v) considerably increased throughout whole profiles of the microcosm (1 m) equipped with passive air venting system (MPAVS). When the simulated landfill gas SLFG flow was 771 g m−3 d−1 and 1028 g m−3 d−1, the O2 concentration in MPAVS increased gradually and tended to be stable at the atmospheric level after 10 days. The CH4 oxidation rate was 100% when the SLFG flow rate was no more than 1285 g m−3 d−1, which also was confirmed by the mass balance calculations. The breathing biocover system with in situ self-oxygen supply can address the problem of O2 insufficient in conventional landfill covers and/or biocovers. The proposed system presents high potential for improving CH4 emission reduction in landfills.