The invention provides a tightening device and method for cable seal kits in a narrow and small space of a box. The device comprises a locking part and a tightening part. The locking part is used forlocking and positioning the multiple cable seal kits at the outer side of a box panel; the tightening part is used for tightening locking nuts on the cable seal kits at the inner side of the box paneland under the locking and positioning effect of the locking part and comprises a tightening sleeve which is matched with the locking nuts and provided with an opening in one side, and a handle is connected to one end of the tightening sleeve. According to the tightening device, the locking part is adopted for locking and positioning the cable seal kits at the outer side of the box panel, and theefficiency of positioning a fixing head at the outer side of the box panel is improved. The tightening part comprises the tightening sleeve which is matched with the locking nuts and provided with theopening in one side, the handle is connected to one end of the tightening sleeve, the locking nuts of the cable seal kits are conveniently tightened in the narrow and small space of the box, and thecable seal kits can be quickly tightened.