A method for preparing an itraconazole formulation including: dissolving a mixture of itraconazole and L-ascorbic acid with a mixed solvent of dichloromethane and methanol, adding a hydroxypropyl methylcellulose and a pluronic F-127 and then dichloromethane into the mixed solvent to obtain a raw material solution; feeding a carbon dioxide into a crystallization autoclave in a supercritical fluid crystallization equipment system through a pressure regulating valve; spraying the solution into the crystallization autoclave via a spray nozzle, separating out composite particles from the solution and collecting the composite particles at a bottom of the crystallization autoclave, and encapsulating the composite particles to obtain a itraconazole formulation with decreased particle size and increased bioavailability.