The mechanical issues on high capacity energy materials (i.e. silicon) prevents their usage as electrode for lithium ion batteries. As alternative, the oxides (i.e. silicon dioxide) are used for a high-expected capacity and strong mechanical stability during cycles. However, the mechanical behavior of amorphous SiO2 during electro-chemical reaction remains largely unknown. Based on the study of the electrochemo- mechanical coupling analysis, we systematically investigate the stress evolution, the electronic structure and the mechanical deformation of lithiated silicon dioxide through first-principles computation and finite element method. The role of oxygen in amorphous silicon oxide was investigated in structural and thermodynamics point of view. The mechanical strength and brittle behavior of SiO2 due to strong Si-O bonds are also studied. These results would provide fundamental perspectives on the chemo-mechanical behavior of silicon dioxide for the practical use.