The invention discloses a bamboo wood preservative made from a natural plant source and a preparation method of the bamboo wood preservative. The bamboo wood preservative comprises, by mass, 2.5%-10% of extract from roots of kudzu vines, 1%-5% of extract from smoke trees, 1%-5% of extract from onions, 30%- 60% of alcohol and the balance distilled water, wherein the sum of the mass percentages of the materials is 100%. The preparation method of the bamboo wood preservative comprises the steps that alcohol and distilled water are mixed according to a mass ratio into ethanol water with the mass percentage of 30%-60%, the extract from roots of kudzu vines, the extract from smoke trees and the extract from onions are added into the ethanol water according to the mass percentages, the mixture is stirred for 30 minutes to 60 minutes in a vacuum decompression sealed tank at the temperature of 50 DEG C to 60 DEG C, the mixture is cooled to the normal temperature, and then a bamboo wood preservative solution containing the extract from roots of kudzu vines, the extract from smoke trees and the extract from onions is obtained, wherein the mass percentage of the extract from roots of kudzu vines, the mass percentage of the extract from smoke trees and the mass percentage of the extract from onions are certain. The bamboo wood preservative made from the natural plant source has the antibacterial function and the insect prevention function and can well restrain bamboo wood rotting fungi, brown rot fungi (Gloeophyllum) and white rot fungi (Coriolus versicolor). The bamboo wood preservative is a totally environmentally friendly material, the preparation technology is simple, energy consumption can be reduced, and compared with a chemical preservative, the bamboo wood preservative is high in safety for the environment.