Disclosed is a syringe comprising: a needle seat (1) an inner sleeve (2) and an injection piston (4). The needle seat (1) is used for installing an injection needle (5). The injection piston (4) is arranged opposite to the needle seat (1) and is used for pushing liquid medicine towards the needle seat (1) and the needle seat (1) and the inner sleeve (2) are nested in a mutually sliding manner. When injecting the inner sleeve (2) is slid to make the inner sleeve overlap with the needle seat (1) to expose the injection needle (5) in order to facilitate injection. When the injection is completed the inner sleeve (2) is slid so as to wrap around the injection needle. After the injection of the syringe the injection piston (4) is slid along the same direction as the injection direction. The needle is wrapped inside the inner sleeve (2) to prevent the needle (5) from being exposed such that it pierces other bodies and causes bacterial infections.
