The utility model relates to a safety needle cylinder, which comprises an outer sleeve, a sleeve arranged in the outer sleeve and a piston rod arranged in the inner sleeve.The outer sleeve has a first annular flange.A second ring flange and a first ring flangeThe holding groove between the second annular flange,The inner sleeve is provided with a needle mounting part for installing the needle head and a positioning part adjacent to the needle mounting part.When the inner sleeve is in a first position,The positioning position of the inner sleeve is outside the holding groove of the outer sleeve.The needle can be pushed out of the outer sleeve by the inner sleeve for injection.When the inner sleeve is pulled back from the first position to the second position,The positioning part of the inner sleeve is in the holding groove of the outer sleeve and is the first part of the outer sleeve.The second ring flange is blocked.The needle remains in the outer sleeve.To increase safety after injection.一種安全針筒，包含有一外套筒、一設於外套筒之內套筒及一設於內套筒之活塞桿。外套筒具有一第一環狀凸緣、一第二環狀凸緣與一位於第一、第二環狀凸緣之間之容置槽，內套筒具有一用以安裝針頭之針頭安裝部與一鄰設於針頭安裝部之定位部，當內套筒位於一第一位置時，內套筒之定位部位於外套筒之容置槽外，使得針頭能藉由內套筒之推動而伸出外套筒進行注射，當內套筒自第一位置被回拉至一第二位置時，內套筒之定位部位於外套筒之容置槽內且被外套筒之第一、第二環狀凸緣給阻擋住，此時的針頭保持於外套筒內，以增加在注射完畢後的安全性。
