The invention discloses a subacidity organic fertilizer for rice planting. Raw materials of the subacidity organic fertilizer comprises animal faeces, rice hull ash, a subacidity auxiliary, seaweed powder, brown rice residues, soybean straw, ferric citrate, ferrous sulfate, potassium chloride, ammonium dihydrogen phosphate, ammonium chloride, sulfuric acid, urea formaldehyde, zinc sulfate, urea, potassium nitrate, ferrous sulfate, calcium superphosphate, copper sulfate, water-soluble silicon, potassium humate, coal dust, perlite, coconut shell flour, lignin, EM fungicide, a modified adhesive and a modified controlled release formulation. The invention further discloses a preparation method of the slightly acid organic fertilizer for rice planting. According to the invention, the prepared slightly acid organic fertilizer for rice planting can provide rich nutrient substances for each stage of rice growth, is high in release efficiency of the nutrient substances, can improve alkalinity and acidity of rice planting soil, provides a more suitable growth pH value for rice and effectively improves yield and quality of rice.