Disclosed is a welding device used for a handheld electric strapping machine, provided with a first motor and a second motor; the first motor is connected to the downward pressing and lifting motion assembly, so as to drive the upper welding member to press downwards and to be lifted upwards; the second motor is connected to the vibration driving assembly, so as to drive the upper welding member to vibrate, achieving heating and welding of packaging straps; the downward pressing and lifting motion assembly is also provided with a limiting member, the limiting member cooperating with a fixing structure on a handheld electric strapping machine and being used for preventing the upper welding member from going beyond the limit when the upper welding member descends to be in place. The welding device uses two motors for respectively and independently driving an upper welding plate to perform downward pressing and welding, thus facilitating manufacturing. After the downward pressing operation is finished, the limiting structure can be automatically locked by using counteracting force, thus ensuring that the upper welding plate is not lifted and loosened when the downward pressing and lifting operating motor is not operating, and ensuring a reliable process of welding.