The invention relates to the technical field of crop fertilizer preparation, and provides a nutrient solution for dendrobium candidum soil-less cultivation and a preparation method thereof. The nutrient solution for dendrobium candidum soil-less cultivation is mainly prepared from the following raw materials: potassium nitrite, monoammonium phosphate, triacontanol, manganese sulfate, copper sulfate, ammonium molybdate, a microbial agent, a tomato extraction solution, a marguerite leaf extraction solution, a folium perillae extraction solution, a cortex dictamni extraction solution, a linaria vulgaris flower extraction solution, an inula flower extraction solution and the like. According to the nutrient solution, the composition is scientific and reasonable, the nutrient solution has the efficacy of sterilization, pest killing and the like, diseases and pests are effectively reduced, nutrient substance absorption of crops is promoted, growth and development are promoted, the survival rate of dendrobium candidum seedlings is significantly improved, the yield of dendrobium candidum is greatly improved, the usage rates of chemicals and chemical fertilizers are reduced, the cost is reduced, thus the economic benefits of dendrobium candidum soil-less cultivation are significantly improved, and moreover, a soil-less cultivation method is simple, easy to operate, safe and environmentally friendly.