This paper presents the structure design and analysis of a novel bistable vibration energy harvester dedicated to direction of gravity. Its unique feature is that the bistability is realized by combining the elastic potential energy of the bridge compliant mechanism (BCM) and the gravitational potential energy of the proof mass. Therefore, its potential energy traps exhibit less inconsistency under the excitation with the direction of gravity. To evaluate the property of the proposed harvester, an analytical model is established. Parametric study is conducted to evaluate the influence of structural parameter. Static structural analysis is conducted to predict the actual performance of the proposed harvester, which is verified by conducting simulation studies.