NOVELTY - A crystalline silicon solar cell back surface field aluminum paste comprises 74 pts. wt. aluminum powder, 20-25 pts. wt. organic bond, 1-4 pts. wt. lead-free glass powder and 0.1-2 pts. wt. additives, where the organic bond comprises terpineol, butyl carbitol, butyl carbitol acetic ester, ethyl cellulose, dibutyl phthalate and sorbitol anhydride stearate. The glass powder comprises bismuth oxide, boron trioxide, bismuth fluoride, silicon dioxide, zinc oxide, aluminum oxide and phosphorus pentoxide. The additive is copper powder with purity larger than 99% and fineness of about 20000 meshes.    USE - Crystalline silicon solar cell back surface field aluminum paste.    ADVANTAGE - The aluminum paste is high in photoelectric conversion efficiency and adhesive force, and has better water-boiling resistance.    DETAILED DESCRIPTION - A crystalline silicon solar cell back surface field aluminum paste comprises 74 pts. wt. aluminum powder, 20-25 pts. wt. organic bond, 1-4 pts. wt. lead-free glass powder and 0.1-2 pts. wt. additives, where the organic bond comprises 40-70 pts. wt. terpineol, 5-10 pts. wt. butyl carbitol, 5-10 pts. wt. butyl carbitol acetic ester, 3-10 pts. wt. ethyl cellulose, 5-15 pts. wt. dibutyl phthalate and sorbitol anhydride stearate. The lead-free powder comprises 30-60 pts. wt. bismuth oxide, 5-15 pts. wt. boron trioxide, 3 pts. wt. bismuth fluoride, 10-20 pts. wt. silicon dioxide, 5-10 pts. wt. zinc oxide, 1-5 pts. wt. titanium oxide, 10-20 pts. wt. aluminum oxide and 1-3 pts. wt. phosphorus pentoxide. The additive is spherical copper powder with purity larger than 99% and fineness of about 20000 meshes. An INDEPENDENT CLAIM is also included for a method for preparing crystalline silicon solar cell back surface field aluminum paste, which involves mixing evenly aluminum powder, organic bonds, lead-free glass powder and additives, rolling the aluminum powder, organic bonds, lead-free glass powder and additives by a three-roll grinder till the fineness is smaller than or equal to 10 microns and viscosity is 30-60 Pa.s.