A highly filled back surface field aluminum paste for point contacts in PERC cells and its preparation method include dissolving ethyl cellulose in organic solvent, stirring under a certain temperature to prepare a homogeneous and transparent organic carrier, adding aluminum powder, nanosized aluminum-boron-antimony alloy powder and auxiliary additive, and three-roller grinding, comprising 70-85 parts by weight of aluminum powder, 1-5 parts by weight of nanosized aluminum-boron-antimony alloy powder, 10-25 parts by weight of organic carrier, 0.1-6 parts by weight of inorganic binder and 0.01-1 part by weight of auxiliary additive.