A preassembled medicine mixer comprises a rotary sleeve (4), a guide sleeve I (3), a guide sleeve II (6), a guide part, a dosing barrel (1), and a dosing double needle (2). The guide sleeve I (3) extends into the guide sleeve II (6) and is connected to the rotary sleeve (4). A guide groove (8) is provided on the side wall of the guide sleeve I (3), and two ends of the guide groove (8) are extended by a distance towards opposite directions. A guide spiral groove (7) is provided on an inner wall of the guide sleeve II (6). The guide part is disposed in the guide sleeve I (3) and has a guide block (9) at the outer side thereof. The guide block (9) penetrates through the guide groove (8) and extends into the guide spiral groove (7). In use, the rotary sleeve (4) is rotated to drive the guide part to rapidly move downwards and push a medicine container (17) an upper needle tip of the dosing double needle (2) pierces a sealing plug on the medicine container (17), and a lower needle tip pierces a diaphragm (23) in an interface (22), so that the medicine container (17) is instantly communicated with an infusion container (14), thereby implementing sterile closeness during the entire process of transportation, storage, butt joint, medicine mixing, and infusion.
