The invention discloses a method for removing iron through external circulation standing and cooling during continuous hot-dipping of zinc and aluminum and relates to the technical field of hot-dip galvanizing. The adopted technical scheme is that: a low-temperature standing zinc pot is arranged on the side of a galvanizing zinc pot, zinc-aluminum melt is driven to pass through a pipe to be led out of the galvanizing zinc pot, so that zinc liquid flows into the low-temperature standing zinc pot, and the process of removing the iron in the zinc liquid is performed in the low-temperature standing zinc pot. The low-temperature standing zinc pot is heated by a resistor, and the temperature difference between the low-temperature standing zinc pot and the galvanizing zinc pot is reasonably controlled, the iron in the zinc-aluminum melt is separated out in the low-temperature standing zinc pot through standing and cooling by using different solubility of iron at different temperatures and density difference between iron-containing cadmia and the zinc-aluminum melt, and the iron-containing cadmia is generated and settled at the bottom of the zinc-aluminum melt; and the zinc-aluminum melt which is subjected to standing and purification passes through a pipe connected with the galvanizing zinc pot to flow back into the galvanizing zinc pot so as to finish the process for removing the iron from the zinc-aluminum melt. The method can be used in and out of the line of hot-dipping of zinc and aluminum, so that the content of the iron in the zinc liquid in the galvanizing zinc pot can bereduced obviously, the quality of coating is improved and the waste of the zinc and aluminum is reduced.