NOVELTY - Preparation of micro magnetic carrier comprises adding particle size of magnetic 90-110 nm iron oxide (Fe3O4, 10-50 g/L), adding 8-20% polyvinyl alcohol solution, and uniformly distributing by ultrasonic oscillation; stirring for 30-50 minutes, adding glutaric dialdehyde solution (2-25 vol.%), pure concentrated hydrochloric acid (1.5 vol.%), and sodium alginate solution (0.5-2 vol.%), stirring for 0.5-1.5 hours, and reacting at 45-55 degrees C; and filtering solution through filter screen, eluting with acetone, ethanol and distilled water to wash, and drying for 24 hours at 45 degrees C.    USE - Method of preparation of micro magnetic carrier used in active sludge method (claimed).    ADVANTAGE - The method accelerates degradation of sewage biochemical reaction rate, and improves sewage treatment efficiency and effect.    DETAILED DESCRIPTION - Preparation of micro magnetic carrier comprises adding particle size of magnetic 90-110 nm iron oxide (Fe3O4, 10-50 g/L), adding 8-20% polyvinyl alcohol solution, and uniformly distributing by ultrasonic oscillation; at 85-95 degrees C, rotating under 500-1500 revolutions/minute, stirring for 30-50 minutes, orderly adding glutaric dialdehyde solution (-25 vol.%), pure concentrated hydrochloric acid (1.5 vol.%), sodium alginate solution (0.5-2 vol.%), stirring for 0.5-1.5 hours, and reacting at 45-55 degrees C; filtering solution through filter screen, with grain diameter of more than 50 mu m micro-magnetic carrier, eluting with acetone, ethanol and distilled water to wash, and drying for 24 hours at 45 degrees C to obtain core surface by magnetic Fe3O4 particle coated porous polyvinyl alcohol layer of granular of 50-250 magnetic carrier. An INDEPENDENT CLAIM is included for an active sludge method using micromagnetic carrier as core comprising sequencing batch reactor with reactor and inoculating medium inlet water quality of biological oxygen demand (BOD)/chemical oxygen demand (COD) of more than 0.3, diameter height ratio of reactor of 1:5-1:10, inoculating medium, with magnetic carrier prepared by magnetic carrier and normal sewage secondary biological treatment active sludge, inoculated active sludge concentration at 2-4 g/L (dry active sludge quality/reactor effective volume), mass ratio of magnetic carrier and active sludge at 1:1-1:3; in water anaerobic stirring-aerobic aerating depositing-water-free, and sequencing batch reactor, each operation period time for 4-8 hours, water inlet time for 1-5 minutes, stirring for 60-120 minutes, aerobic aeration for 150-250 minutes, depositing for 5-15 minutes, and draining for 3-10 minutes, operating cycle exchange volume of 60-85%, with field magnetic carrier absorbing at bottom of the reactor to avoid loss, cultivating as core micro-magnetic carrier the fossilization sludge, and closing electromagnetic field.