The invention relates to the technical field of artificial cultivation of Chinese medicinal materials, in particular to a method for preparing a planting substrate used in the artificial cultivation of a Chinese medicinal material, i.e. dendrobium officinale. Currently, the substrates used in the artificial cultivation of dendrobium officinale mainly are tree barks, saw dust, water mosses, peat soil and river sand, wherein the substrates most suitable for growth of dendrobium officinale are the water mosses, the tree barks and the saw dust. The water mosses can be used after being washed and sterilized simply, but have higher price so that the planting cost cannot be accepted by most manufacturers. Compared with the water mosses, the tree barks and the saw dust have obvious advantages on the price, but the tree barks and the saw dust need to be subjected to fermentation treatment before being used and in the fermenting process, the fermentation of the tree barks is more difficult than that of the saw dust. The method can process the saw dust more easily and solve the substrate problem in the planting process of the dendrobium.