Disposable injection needle

A disposable injection needle, comprising:

• a needle seat, wherein the needle seat is provided with a needle tube extending axially therethrough;
• a first sheath, wherein one end of the first sheath is connected to one end of the needle seat to form an accommodating space between the first sheath and the needle seat, and the other end of the first sheath has a first opening;
• a second sheath, wherein one end of the second sheath is located in the accommodating space, and the other end of the second sheath has a second opening and protruding from the first opening;
• a part of the second sheath is located in the accommodating space in an axially slidable manner;
• an inner core, wherein the other end of the inner core is provided with a third opening, and the needle tube axially extends through the third opening and is adapted for being exposed via the second opening;
• and
• a spring;
• wherein:
• the one end of the second sheath is engaged with the inner core by sleeving, and is adapted for retracting towards the accommodating space to expose the needle tube against an elastic force of the spring based on an external force;
• the spring is adapted for providing an elastic force to make the second sheath and the inner core move axially towards the outside of the accommodating space together;
• an inner wall of the first sheath is provided with a first engagement structure, and the second sheath is provided with a second engagement structure engaged with the first engagement structure;
• based on the movement of the second sheath into the accommodating space, the inner core rotates from a first circumferential position to a second circumferential position, and at the second circumferential position, the inner core is adapted to be abutted by the spring and move in a direction away from the accommodating space to push the second sheath;
• and
• at the second circumferential position, the second engagement structure is adapted to pass over the first engagement structure in a direction away from the accommodating space, and the first engagement structure is adapted to prevent the second engagement structure that has passed over the first engagement structure from moving further in a direction toward the inside of the accommodating space.