The invention discloses a method for underload recovery of methyl iodide from low-pressure tail gas in acetic acid production. The method comprises the following steps: (1) cooling methanol, from the bottom of a regeneration column, in a methanol barren liquor cylinder by a barren liquor cooler, and then transferring cooled methanol into a low-pressure absorbing column together with fresh methanol by a barren liquor methanol pump; (2) feeding the liquid from the bottom of the low-pressure absorption column and part of the mixture of methyl iodide and methanol condensed by a condenser of the regeneration column into an absorbed methanol storing cylinder, reflowing the other part of the mixture of methyl iodide and methanol condensed by the condenser of the regeneration column to the top part of the regeneration column, and transferring the non-condensable gas from the condenser of the regeneration column to a gas balance pipeline; and (3) transferring part of iodine-containing methanol pregnant solution from the absorbed methanol storing cylinder into a reacting kettle by an absorbed methanol feeding pump, and transferring the other part of the dine-containing methanol pregnant solution into the regeneration column by a methanol adding pump of the regeneration column. The method has the effects that the layering effect of a layering device is greatly improved, the proportion of heavy phases is improved, and the balance of iodide in the system can be ensured.