The invention discloses a method for preparing a nanometer hydroxycamptothecin crystal freeze-dried powder preparation. Main raw materials of the nanometer hydroxycamptothecin crystal freeze-dried powder preparation consist of an active raw material, namely hydroxycamptothecin, phospholipids, a surfactant, namely poloxamer 188 or polyethylene glycol stearate-15, and a freeze-dried auxiliary material excipient. The method for preparing the nanometer hydroxycamptothecin crystal freeze-dried powder preparation comprises the following steps: after the hydroxycamptothecin is added into an alkaline solution to be dissolved, the phospholipids are added in an ultrasonic water bath, and the poloxamer 188 or the polyethylene glycol stearate-15 is added into the mixture under magnetic stirring to be dissolved; the pH value of glacial acetic acid is adjusted to be between 4.0 and 6.0, and hydroxycamptothecin crystals are precipitated; and then the high-pressure homogenization is performed to obtain a nanometer hydroxycamptothecin crystal suspension, and then the freeze-dried auxiliary material excipient is added to be freezely dried to obtain the nanometer hydroxycamptothecin crystal freeze-dried powder preparation. The method is simple and easy to operate. Nanometer crystal freeze-dried powder has the advantages of high dispersity, good stability and so on. The average size of the crystals is 355.6nm, the average content of the hydroxycamptothecin in a sample is 98.5 percent of labeled amount, and the effect of inhibiting and killing liver cancer and gastric cancer cells of the preparation is remarkably stronger than that of a hydroxycamptothecin injection.