The invention belongs to the technical field of soil improvement and particularly relates to an ecological soil conditioner capable of improving acid soil and a preparation method. The ecological soil conditioner comprises raw materials in parts by weight as follows: 30-60 parts of carbonized distillers' grains, 10-20 parts of industrial and agricultural waste, 10-15 parts of sargassum, 10-15 parts of water hyacinth, 5-10 parts of plant ash, 5-15 parts of nano-modified clay, 5-10 parts of sodium alginate, 1-10 parts of tamarind polysaccharide gum, 1-5 parts of chelated secondary elements and trace elements and 0.1-3 parts of graphene oxide. The ecological soil conditioner can regulate the pH value of the soil, promote granular structure formation of the soil, improve the physical and chemical structures of the acid soil, increase organic matter content of the soil, improve the moisture and fertilizer retention capacity, improve physical characteristics of the soil, creates a good ecological environment for plant growth, is excellent, meets the organic and pollution-free agricultural development trend and has larger popularization and application value.