Disposable scalpel blade assembly and supporting reusable handle. The blade assembly includes a blade, blade holder and blade shield. The blade holder has a flexible arm at the rear-end, which has a protrusion-block at the arm end. The blade shield inner wall has clearance opening for the protrusion-block. When the handle is inserted, the protrusion-block extends into the clearance opening with sideward movement, so the blade and blade holder are connected. After the handle is pulled-out, the protrusion-block misaligns with the clearance opening and cannot make sideward movement so the handle cannot connect again. The blade holder first sliding channel is provided with a first front locking channel at its front-end and a deadlock channel is set in front of the first front locking channel. When the handle is pulled-out after use, the first protrusion of the blade shield shall fall into the deadlock channel to enter the deadlocking state.