Multi-walled carbon nanotubes (MCNTs) were doctor-bladed on Ti meshes to prepare flexible counter electrodes for quantum dots sensitized solar cells. PbS was decorated on MCNTs surfaces through successive ionic layer adsorption and reaction to improve the catalytic activities of redox reactions in polysulfide electrolytes. The electrochemical catalytic activities of obtained PbS/MCNT counter electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization curves. After optimization, the QDSCs based on PbS/MCNTs counter electrodes delivered photovoltaic conversion efficiencies reaching 6.39%, values 40% higher than those of pure MCNTs CEs.