The invention relates to the field of medicines, and particularly discloses a premixing method for powder agents and aqueous solutions. According to the premixing method for the powder agents and the aqueous solutions, a premixing transfusion bag is used, sterile preparation of powder agents and medicines can be achieved through a mixing mechanism in the premixing transfusion bag, and potential safety hazard of transfusion is reduced; meanwhile, through effective linkage of a sensation mechanism and a blocking mechanism inside the bag, the proportions of the aqueous solutions and the powder agents can be automatically controlled; in the preparation process, the aqueous solutions and the medicines are not transferred, so that the hidden danger of bacterial infection of the medicines is greatly reduced; a finally prepared finished medicine can be directly used through the premixing transfusion bag. By adopting the scheme, the mixing security of the aqueous solutions and the powder agents can be improved.