We report on electronic properties of water-filled fullerenes [H2O(n)@C60, H2O(n)@C180, and H2O(n)@C240] under mechanical deformation using density functional theory. Under a point load, energy gap change of empty and water-filled fullerenes is investigated. For C60 and H2O(n)@C60, the energy gap decreases as the tensile strain increases. For H2O(n)@C60, under compression, the energy gap decreases monotonously while for C60, it first decreases and then increases. Similar behavior is observed for other empty (C180 and C240) and water-filled [H2O(n)@C180 and H2O(n)@C240] fullerenes. The energy gap decrease of water-filled fullerenes is due to the increased interaction between water and carbon wall under deformation.