The invention provides a soil conditioner suitable for southern red soil and a preparation method, and belongs to the technical field of soil conditioner preparation and utilization. The soil conditioner is composed of, by mass, 12.5-25% of bio-active humic acid, 5-11.5% of chicken manure, 4-12% of tobacco waste, 2.5-7.5% of corn straw, 3-9% of rice straw, 5-11.5% of grass coals, 5-12.5% of sucrose filter mud, 1-6% of calcium superphosphate, 1-4.5% of urea, 2-6% of potassium sulphate, 9-17.5% of calcium magnesium phosphate, 0.5-2.5% of manganese sulfate, 0.5-2.5% of ferrous sulfate, 0.5-3% of zinc sulfate, 0.5-2.5% of ammonium molybdate, 2.5-7.5% of boric acid, 0.5-4% of BFA microbial agents and 1.5-4% of bentonite, and the sum of all the components is 100%. The soil conditioner takes the organic nutrient humic acid as the main component and contains a large quantity of readily oxidized organic matter, active groups and exchangeable magnesium, therefore, the physical and chemical properties of the acid soil can be obviously improved, comprehensive and reasonable nutrients are supplied to crops, the crop growth is promoted, the crop quality and yield are improved, the arable soil quality can be comprehensively improved, and the conservation soil fertility is improved.