The invention provides a back passivation solar cell back silver paste and a preparation method thereof. The paste includes micrometer silver powder, nanometer silver powder, inorganic glass powder, and an organic carrier, the inorganic glass powder is formed by a 80-92 wt% component X and a 8-20 wt% component Y, the component X is PbO and / or Bi2O3, and the component Y is B2O3. According to the back passivation solar cell back silver paste and the preparation method thereof, the back silver paste is printed on the backside of a back passivation silicon substrate, a smooth and compact back electrode can be formed, the adhesion between the back electrode and the silicon substrate is good, a welding pulling force test with a photovoltaic welding strip is in accordance with the requirement of the current photovoltaic industry, and the photoelectric conversion efficiency of solar cells prepared by employing the back silver paste is effectively improved.