The invention discloses a silkworm excrement and shell ecologic acidic soil conditioner and a preparation method thereof, and belongs to the technical field of agriculture soil fertilizers. The silkworm excrement and shell ecologic acidic soil conditioner is prepared from, by weight, 20-90 parts of shells and 10-80 parts of silkworm excrement. Synergism of shell powder and silkworm excrement after the shell powder and the silkworm excrement are mixed, co-fermented and combined is found in the invention, so the utilization of calcium in the shell powder by the acidic soil is greatly improved, the soil acidity improvement effect of the conditioner is substantially better than the total acidity improvement effect reached by individual use of the silkworm excrement and the shell powder; and the conditioner disclosed in the invention improves the acidic soil improving effect of the silkworm excrement and the shell powder, improves the absorption of nutrition in the silkworm excrement and shells by crops, and increases the output of crops.