The invention relates to a method for performing raw soil greening on coast saline land through a biological modifier containing fly ash. The biological modifier comprises the following components in weight part: 8-12 parts of ceramsite, 11-15 parts of vermiculite, 1-5 part of fly ash, 0.5-2 parts of iron chloride, 0.5-2 parts of calcium dihydrogen phosphate, 0.2-1 parts of formic acid, 1-4 parts of amino acid salt, 2-6 parts of fermented sheep manure, 2-7 parts of capsicum straw powder, 0.3-1 parts of compound sodium nitrophenolate, 0.3-1 parts of amino-oxyacetic acid, 0.3-1 parts of soybean germ extract, 0.5-2 parts of potassium ferrocyanide, 0.2-0.5 parts of cellulose cellulose grafted acrylic acid salt, 0.1-0.5 parts of halomonas, 0.1-0.5 parts of Bacillus subtilis, 0.1-0.5 parts of azotobacter vinelandii, 0.1-0.5 parts of Aspergillus oryzae and 0.1-0.5 parts of Trichoderma longibrachiatum.