NOVELTY - Nitrite in cultivation sewage is degraded by preparing 20-30 g/L nitrobacteria solution, mixing with embedding liquid, dropping to crosslinking agent, crosslinking at pH 6-6.5 for 12-16 hours, filtering out immobilized nitrobacteria, washing with normal saline, activating in culture medium having pH 7.2-7.6 with aeration at 27-30 degrees C for 12-15 hours, filtering out activated immobilized nitrobacteria, washing with normal saline, blending with 5-10 mm dry wood coal, uniformly fixing in gauze reaction bag and fixing prepared reaction bag in surface water at 2-4 m away from aerator diameter.    USE - Method for degrading nitrite in cultivation sewage (claimed).    ADVANTAGE - The method is fast, persistent, has stable nitrite degradation effect, maintains high biological activity for a long time and utilizes reusable reaction bag having simple preparation at a low cost.    DETAILED DESCRIPTION - Nitrite in cultivation sewage is degraded by:    (A) letting stand fermented nitrobacteria solution for 8-14 hour, removing supernatant and diluting collected concentrated bacteria solution with normal saline to form 20-30 g/L solution;    (B) mixing nitrobacteria solution to embedding liquid comprising aqueous mixture of (mass%) polyvinyl alcohol (8-10), sodium alginate (1-3) and silicon dioxide (1-2) at volume ratio of 1:1 to 1:3, dropping to a crosslinking agent comprising mixture of 2 mass% calcium chloride solution and saturated boric acid solution at volume ratio of 1:1 to 1:3, at crosslinking agent to embedding solution volume ratio of 2:1 to 4:1, crosslinking at pH 6-6.5 for 12-16 hours, filtering out immobilized nitrobacteria and washing 2-3 times with normal saline;    (C) activating immobilized nitrobacteria in culture medium comprising mixture of (g) sodium bicarbonate (1.2-1.8), sodium nitrite (0.3-0.6), magnesium sulfate heptahydrate (0.1-0.2), dipotassium hydrogen phosphate (0.1-0.2), sodium chloride (0.1-0.3) and ferrous sulfate heptahydrate (0.01-0.1) in tap water (1000 ml) having pH 7.2-7.6, with aeration at 27-30 degrees C for 12-15 hours, filtering out activated immobilized nitrobacteria and washing 2-3 times with normal saline;    (D) blending activated immobilized nitrobacteria with 5-10 mm dry wood coal at mass ratio of 1:1 to 1:3 and uniformly fixing in gauze reaction bag; and    (E) fixing prepared reaction bag (100-150 bag/acre) in surface water at 2-4 m away from aerator diameter.