The invention discloses a method for improving acidified soil and enhancing 
soil fertility by the aid of 
nitrogen-fixation 
cyanobacteria. The method includes steps of 1), selecting 
anabaena to be usedas 
nitrogen-fixation 
cyanobacteria application 
algae species, and carrying out step-by-step extended culture; 2), deeply plowing 
crop rotation fields by the depths of 15-20 cm at early-season rice 
transplanting earlier stages in double-
cropping rice 
modes at first, 
transplanting rice, then applying 
nitrogen, 
phosphorus and 
potassium fertilizers, inoculating the nitrogen-fixation 
cyanobacteria according to a quantity of 3-5 kg of fresh alga for each mu, harvesting early-season rice, then shallowly plowing the 
crop rotation fields by the shallow plowing depths of 5-10 cm, planting late rice, and applying the nitrogen-fixation cyanobacteria and nitrogen, 
phosphorus and 
potassium fertilizers according to the same process; alternately, deeply plowing the 
crop rotation fields by the depths of 15-20 cm at first at rice 
transplanting earlier stages in single-
cropping rice 
modes, transplanting the rice, then applying the nitrogen, 
phosphorus and 
potassium fertilizers, and inoculating the nitrogen-fixation cyanobacteria according to a quantity of 5-7 kg of fresh alga for each mu. The method has the advantages that the application amount of nitrogen fertilizers can be reduced by 50%, the nitrogen-fixation cyanobacteria can be fed into 
red soil along with deep plowing or shallow plowing, the 
organic matter content of the 
red soil can be increased after the nitrogen-fixation cyanobacteriais decomposed, and accordingly the 
soil fertility level of the 
red soil can be comprehensively enhanced.