The invention relates to a preparation method for bortezomib for injection. The preparation method comprises the following steps: (1) polylactic acid and tertiary butanol are weighed, and a certain quantity of injection water is added for dissolving to obtain a polylactic acid and tertiary butanol mixed solution; (2) bortezomib raw materials are weighed, added in the mixed solution, and stirred until the raw materials are dissolved totally; (3) mannitol is weighed, added in the solution with the dissolved raw materials, and the injection water is added to account for 70% of the total amount, then is quickly stirred until the mixture is completely dissolved; (4) 5 g of activated carbon is added and stirred for 20 minutes, then is filtered out; (5) the injection water is added to reach 9.5 L; the pH value is regulated to 4.0-7.0 by using sodium hydroxide or hydrochloric acid; then the injection water is added until the total amount achieves 10 L; (6) the vacuum freeze drying technique is adopted for freeze-drying after filling; the freeze-drying technique is as follows: the pre-freezing temperature is kept for -40 DEG C for 3 hours; the sublimation drying time is 16 hours; the resolve drying time is 4 hours; the total time is 23 hours.