The invention discloses a method for preparing a negative pressure solvent of water-soluble nano-taxol powder. The method is characterized by comprising the following steps of: preparing the solution of 1 to 100 mg/ml taxol anhydrous alcohol or N-methyl-pyrrolidone; in a negative pressure cavitation stirring state, mixing the solution and anti-solvent water in an amount which is 3 to 8 times volume of the solution at the temperature of 4 to 40 DEG C and crystallizing; filtering mixed liquid by using a plate frame; drying an obtained filter cake at the temperature of 70 to 105 DEG C; crushing the dried filter cake to obtain the water-soluble nano-taxol powder; and recovering filtrate solvent for recycling. The taxol powder obtained by the method has uniform grain size distribution, high water solubility, high yield and low cost, and is easy to industrialize.