The invention discloses a method for one-time separation and extraction of dendrobe polysaccharide, dendrobine and erianin from dendrobium candidum. The method for extraction of dendrobe polysaccharide, dendrobine and erianin from dendrobium candidum comprises the steps of crushing of dendrobe, enzymatic hydrolysis, ultrasonic extraction, microfiltration, ultrafiltration and nano-membrane concentration, solid-liquid separation, vacuum cryogenic distillation, solvent extraction, solvent recovery, recrystallization, vacuum low-temperature drying and purification in the carbon dioxide supercritical fluid, thereby obtaining the dendrobe polysaccharide, dendrobine and erianin. The prepared product has good color, good solubility and high active ingredients.