The utility model relates to a solar cell device based on strain type heterojunction quantum dots and further relates to a preparing method thereof, belonging to the field of solar cell materials. The cell device includes at least two Ge/Si quantum dot structure layers growing on a doped silicon-based substrate, each Ge/Si quantum dot structure layer is formed by a Si thin layer including Ge quantum dots having the diameter of 2-7nm, the thickness of the innermost Si thin layer is 2-4nm, and the thickness of the thin layers is gradually increased layer by layer, the outmost quantum dot structure layer is a SiO2 cover thin layer for filling the gaps of the quantum dots to form a quantum dot array filling film multilayer structure, a silicon doping layer protection film having the thickness of 10-20nm grows outside the cover thin layer, and electrodes grow on the outer surfaces of a silicon doping layer and the silicon-based substrate. The energy zone of the solar cell device is expanded to be in the range of 0.4-0.22eV, the corresponding conversion efficiency is in the range of 55-57%, and compared with the conversion efficiency in the prior art, the conversion efficiency is improved by more than 7%, so that the photoelectric conversion efficiency of a solar cell is greatly improved.