The crystalline form of Bimatoprost in the prior art is insoluble in solvents such as ethyl acetate, tert-butyl acetate, dichloromethane and methyl isobutyl ketone etc. at low temperature, thus when Bimatoprost of the crystal morphology in the prior art is crystallized, it is dissolved at the temperature near the boiling point or boiling temperature of the solvents and then cooled for recrystalliz