NOVELTY - Preparation of slow-release compound fertilizer comprises sun-drying water hyacinth straw, mixing rice and wheat straw, soybean straw, peanut straw, sunflower straw, and water hyacinth straw, cutting, and crushing; adding with cellulase and mixing; adding gelatin to water, dissolving, adding water, stir-heating, taking gelatin solution, mannose polysaccharide solution, and aqueous polyvinyl alcohol solution, and stir-heating; adding glycerin and polysorbate and mixing; adding crosslinking agent; adding product in third step, stirring, standing, and degassing; and film-forming and drying.    USE - Method for preparing slow-release compound fertilizer (claimed).    ADVANTAGE - The fertilizer solves problems such as not containing sufficient nutrient substances needed by crops, straw burning wastes resources, and damage lands, saves resources, improves yield, sufficiently supplies nutrients, and has low cost.    DETAILED DESCRIPTION - Preparation of slow-release compound fertilizer comprises:    (A) sun-drying water hyacinth straw, taking 10-20 pts. wt. rice and wheat straw, 25-30 pts. wt. soybean straw, 15-20 pts. wt. peanut straw, 20-30 pts. wt. sunflower straw, and 20-30 pts. wt. water hyacinth straw, mixing, cutting, and crushing to straw fiber length of 3-5 cm;    (B) mixing fiber straw with cellulase at ratio of 1:20 and high speed stirring for 20-30 minutes at 800 revolutions/minute (rpm);    (C) adding 30 g gelatin to 10 mL water, dissolving, adding 900 mL water, stir-heating, taking 30-40 wt.% gelatin solution, 10-30 wt.% 0.5 mol/L mannose polysaccharide solution, and 30-60 wt.% 1.3 mol/L aqueous polyvinyl alcohol solution, and stir-heating at 50 degrees C for 1-5 minutes;    (D) taking 100-150 mL mixed solution, adding 20-30 mL glycerin and 3-5 mL 1 g/L polysorbate, and mixing at 300 rpm;    (E) adding 3-5 g crosslinking agent to form sustained release coating material, where crosslinking agent comprises 50-60 wt.% dicumyl peroxide and 40-50 wt.% 2,5-dimethyl-2,5-di-t-butylperoxy-hexane;    (F) adding product in third step at mass ratio of 1:3, stirring for 30 minutes at 600 rpm, standing, and degassing for 2-5 hours; and    (G) film-forming and vacuum drying.