NOVELTY - Fertilizing purple-skin dendrobe comprises (i) selecting fertilization period, (ii) selecting fertilizer application period, (iii) selecting fertilizer, and (iv) controlling fertilizer application concentration, where in the step (iii), selecting fertilizer rich in nitrogen, phosphorus and potassium; the fertilizer raw material is composed of e.g. nitrogen, phosphorus, potassium, calcium, and iron. In the fertilizer application concentration controlling step, sprinkling or spraying biogas slurry and water, applying farmyard manure, and removing fermentation filter residue.    USE - The method is useful for fertilizing purple-skin dendrobe (claimed).    ADVANTAGE - The method avoids improper dendrobe rooting, overcomes poor growth condition, and is easy to implement and use.    DETAILED DESCRIPTION - Fertilizing purple-skin dendrobe comprises (i) selecting fertilization period, (ii) selecting fertilizer application period, (iii) selecting fertilizer, and (iv) controlling fertilizer application concentration, where in the step (iii), selecting fertilizer rich in nitrogen, phosphorus and potassium, and also further needs calcium, iron, zinc, sulfur, boron, manganese, and copper trace elements; the fertilizer raw material is composed of 23-26% nitrogen, 12-16% phosphorus, 12-18% potassium, 1-3% calcium, 3-6% iron, 2-3% zinc, 0.3-0.6% sulfur, 0.2-0.5% boron, 0.1-0.3% manganese, 0.1-0.3% molybdenum, and 0.1-0.6% copper. In the fertilizer application concentration controlling step: sprinkling or spraying 1 part biogas slurry and 2-5 parts water, applying farmyard manure soaked in water, removing fermentation filter residue, taking upper clear liquid and mixing the same with water and spraying, using ternary complex fertilizer diluting into 0.3% concentration solution, or using urea and potassium dihydrogen phosphate according to 1.5:1.5, preparing spraying solution of 0.2%, or using equal amount of urea, calcium, potassium chloride, and diluting into 0.2% solution for spraying, or using 0.4% potassium nitrate spraying solution.