A trocar includes a paracentesis knife and a trocar housing. The paracentesis knife includes a base and a puncturing portion, wherein the puncturing portion has a bump radially extended from the outer surface of the puncturing portion, and a tip end. The trocar housing includes a first pipe assembly, a second pipe assembly, a fixing base, and an air cell. The second pipe assembly can moved back so that the first pipe assembly can be received in the second pipe assembly. The fixing base is fixed on the second pipe assembly, and includes a guiding groove and a key groove. When the bump is put into the guiding groove and then rotating the paracentesis knife, the bump is into the key groove and fixing the paracentesis knife and the fixing base. Therefore, the trocar housing can be moved in an axial direction of the paracentesis knife when the paracentesis knife moves axially.一種穿刺器,包含穿刺器械及套接件。穿刺器械包含底座及穿刺部,且穿刺部包凸塊及尖端,凸塊由穿刺部的外表面向外徑向延伸。套接件包含氣壓座、第一套管組件、第二套管組件、固定座、以及氣囊。第二套管組件可收縮,使第一套管組件容置於第二套管組件中。固定座固定於第二套管組件,且固定座的內壁具有導引槽及鍵槽,導引槽的深度大於鍵槽,導引槽與鍵槽連通,當穿刺器械之凸塊由導引槽進入,經旋轉使得凸塊卡設鍵槽後,穿刺器械與固定座固定,穿刺器械帶動固定座沿穿刺器械的一長軸方向上移動。10‧‧‧穿刺器械11‧‧‧底座13‧‧‧穿刺部131‧‧‧凸塊133‧‧‧尖端27‧‧‧固定座271‧‧‧通道273‧‧‧內緣壁277‧‧‧鍵槽
