Abstract: A protecting cap structure for the needle of a syringe, wherein, the structure is provided with a protecting sleeve having a receiving space for receiving a needle. The protecting sleeve is comprised of a foldable cover and a cylindrical extendible member connected with each other; the cylindrical extendible member is a hollow cylinder, the shank of the cylindrical extendible member has a compression portion; a pair of foldable portions are provided in neighboring to the compression portion; the foldable cover is in the shape of a semi-cylinder, one end of the foldable cover is connected with the cylindrical extendible member, in order that when the cover is folded to close, it cooperates with the cylindrical extendible member to envelop and fast envelop the needle to prevent the needle from accident stabbing.