The invention relates to a rice fulvic acid polyelement composite liquid base fertilizer taking concentrated biogas slurry as a base solution, which is prepared from the following raw materials in portion by weight: 210 to 215 portions of ammonium polyphosphate, 55 to 60 portions of urea, 305 to 310 portions of potassium chloride, 30 to 32 portions of borax, 10 to 11 portions of zinc sulfate, 10 to 12 portions of suspending agent, 335 to 310 portions of the concentrated biogas slurry and 45 to 50 portions of fulvic acid. The fertilizer contains 357 to 374 g/L of macroelement, 51 to 54 g/L of the fulvic acid, and 12 to 23 g/L of water-insoluble matters; and the pH value of the fertilizer subjected to dilution by 250 times is 6.0 to 6.2. The production of the fertilizer comprises the following steps: comprehensive analysis of soil agricultural-chemistry characteristics, rice fertilization experiment, calculation of fertilizer proportion, selection of raw materials, material preparation, and mixing and preparation; and before the rice transplantation, the fertilizer is applied with a dosage of 132 kilogram/mu when irrigation and field harrowing are performed at the same time. The fertilizer uses biogas slurry, is free from generating secondary pollution, and has reasonable and even application; and the invention provides a base fertilizer containing the macroelement, microelement and fulvic acid active substances for rice to promote the growth and production increase of the rice.