A tab welding method, comprising: first, using a toothed welding head to perform first welding on a positive tab and a negative tab which are provided in a stacked manner, so as to form a tab body (30) having a first welding mark region (31), so that the positive tab and negative tab which are provided in a stacked manner are in solid-phase connection; then using a toothless welding head (40) to perform flat welding to form a second welding mark region (32), so as to shape and flatten an uneven region formed after the first welding. Also provided are a battery cell prepared by means of the tab welding method, a battery having the battery cell, and an electric device having the battery. By means of the method, gaps between multiple stacked tabs can be eliminated.