NOVELTY - Multifunctional liquid biological fertilizer comprises 10-12 wt.% amino acid compound, 35-52.5 wt.% vinegar plant, 2-2.4 wt.% amino acid fertilizer containing trace element and 0.16-2 wt.% selenium, 8-10 wt.% oligochitosan containing 0.2-0.25 wt.% selenium and titanium, and 0.2-0.25 wt.% hydrogen peroxide.    USE - Multifunctional liquid biological fertilizer used for promoting crop photosynthesis and crop growth.    ADVANTAGE - The method improves crop fertilizer absorption and utilization and quality of agricultural product, increases crop resistance to disease and yield, and reduces and eliminates heavy metal in crop and pesticide residue.    DETAILED DESCRIPTION - Multifunctional liquid biological fertilizer comprises 10-12 wt.% amino acid compound, 35-52.5 wt.% vinegar plant, 2-2.4 wt.% amino acid fertilizer containing trace element and 0.16-2 wt.% selenium, 8-10 wt.% oligochitosan containing 0.2-0.25 wt.% selenium and titanium, and 0.2-0.25 wt.% hydrogen peroxide. The biological fertilizer is produced by:    (A) (i) taking amino acid, vegetable vinegar and amino acid fertilizer containing iron, copper, molybdenum, boron ions chelate-forming amino acid trace element complexes; (ii) fermenting with microorganisms comprising glutamic acid, cystine, cysteine and amino acid glycine; (iii) taking plant vinegar i.e. wood vinegar, bamboo vinegar and grass straw vinegar; (iv) adding with 6% disodium EDTA and stirring for 60-180 minutes using electric mixer; and (v) mixing 20 wt.% amino acid-containing solution, 70 wt.% plant vinegar, 6 wt.% disodium EDTA and 4 wt.% trace element;    (B) weighing 4000-6000 g 80-100 meshes chitosan powder at deacetylation degree of not greater than 80%, placing in reaction container, adding with 30000 mL tetrafluoroethylene and 5000-8000 mL 15-30% aqueous hydrogen peroxide, soaking in aqueous hydrogen peroxide solution, oxidative degrading at room temperature for 60-180 minutes, microwave irradiating at 2450 MHz and power of 5000 W for 3-5 minutes, and diluting with 40 wt.% water to obtain chitosan oligosaccharide solution;    (C) taking 9887 mL 40% chitosan oligosaccharide solution, placing in 30000 mL stainless steel reaction container, adding with 113 g chemically pure selenium dioxide powder, and mixing at 60-80 degrees C for 60-180 minutes;    (D) weighing 1000 g titanium citrate containing 10-12% titanium, placing in 30000 mL stainless steel reactor container, adding 8600 mL water, stirring for 10-15 minutes, adding 400 mL 25% aqueous hydrogen peroxide solution, mixing, and standing at room temperature to obtain mixture containing 0.8 wt.% selenium, 1 wt.% titanium and 1 wt.% citric acid; and    (E) (i) taking 40% mixture, adding with peroxide titanate complexes at weight ratio of 1:1, placing in stainless steel reaction container, stirring for 60-180 minutes, formulated as selenium Se0.4%, titanium Ti0.5%, containing peroxide 0.5% hydrogen, 20% of the chitosan oligosaccharide solution containing; and (ii) mixing with amino acid fertilizer solution at weight ratio of 1:1-1.5, placing in stainless steel reaction container, and stirring for 60-180 minutes.