The utility model relates to the technical field of nuclear power station maintenance, in particular to a handheld online machining device for cutting and forming the end part of a neutron flux tube,which mainly solves the problems of complex cutting and forming machining process and high operation difficulty of the end part of a thimble tube. The tool rest is composed of a clamping device, a tool rest body and a driving device, the two ends of the tool rest body are fixedly connected with the clamping device and an axial feeding device, and the other end of the axial feeding device is connected with the driving device. The clamping device comprises a supporting frame, a connecting disc and a clamping head. The knife rest comprises a connecting frame, an axial feeding ring, a knife handle, a beveling knife and a section knife. The knife rest is fixedly connected with the clamping device and the driving device. The driving device comprises a motor, a shell and a lithium battery. Aftercutting and forming machining, the end face flatness and perpendicularity, the welding groove form, the cylindricity, the coaxiality, the surface smoothness and the like of the finger sleeve can all meet the requirements, and manual operation can be completely replaced.