The invention discloses a preparation method of an effective part of dendrobium officinale. The method comprises steps as follows: firstly, extracting fat-soluble extracts represented by bibenzyl from the dendrobium officinale with a high-concentration alcohol-water system, refining the extracts with a macroporous resin method to obtain a total bibenzyl effective part with the bibenzyl content higher than 50%, and preparing dregs of the extracts into dendrobium officinale total polysaccharides with water extraction and alcohol precipitation methods; drying and evenly mixing the total bibenzyl effective part and the dendrobium officinale total polysaccharides obtained in two steps to obtain a dendrobium officinale total effective part extract. According to the method, the defect of the extremely low extraction rate of dendrobium officinale fat-soluble active ingredients represented by the bibenzyl with traditional methods such as a water decoction method, a tea making method and the like is overcome, the utilization efficiency of the effective part of the dendrobium officinale is improved substantially, pharmacological anti-oxidation animal experiments and anti-tumor cytotoxicity experiments prove that the activity of the effective part is significantly higher than that of traditional aqueous extracts, and the effective part has the characteristics of high extraction rate and high activity.