The effect of moisture content on the electrochemical performance of a LiNi1/3Co1/3Mn1/3O2 (NCM)/graphite battery was investigated by studying different moisture contents of a positive-NCM/Li half cell, negative-graphite/Li half cell and positive-NCM/negative-graphite cell. The moisture content influences the oxidized decomposition of electrolyte. A higher moisture content results in a lower oxidized decomposition potential. The product of oxidized decomposition deposits on the surface of positive, and results in an increase of positive resistance (R f). The NCM structure is stable with change in moisture content. Moisture joined in the formation reaction and changed the components of the solid electrolyte interphase film in negative. The high moisture content resulted in a thick, porous, non-dense solid electrolyte interphase film. Cycle testing of the NCM/graphite cell shows that a moisture content in the negative electrode influences capacity fading more significantly than in the positive electrode. The reason for capacity fading was studied by three-electrode technology. The increase in negative impedance is the main reason for an increase in battery impedance. The battery impedance increased rapidly when the moisture content in the negative electrode was high. This resulted in accelerated capacity fade.