Freeze-drying method of pemetrexed disodium

The invention discloses a freeze-drying method of pemetrexed disodium, a pemetrexed disodium solution is prepared into a freeze-dried powder injection, and the freeze-drying method comprises the following steps: 1) pre-freezing; the pre-freezing adopts a process of firstly cooling, then heating and then cooling, and the highest heating temperature is less than or equal to-10 DEG C; 2) sublimation drying; six temperature gradients are set for sublimation drying, and the temperature rise amplitude between the temperature gradients ranges from 5 DEG C to 15 DEG C; the vacuum degree is controlled to be 10-15 Pa in the sublimation drying process; 3) desorption drying; the vacuum degree is controlled to be 2-4 Pa in the desorption drying process. According to the pre-freezing annealing process obtained through experimental verification, precise sublimation drying temperature parameter gradient setting and provision of the vacuum degree of the desorption drying stage, the product appearance can be effectively improv