The invention relates to the field of electronic element integrated board welding auxiliary equipment, in particular to a gas-phase reflow soldering device. The gas-phase reflow soldering device comprises a sealed steam box, a conveying pipeline and a conveying belt, wherein the conveying pipeline is partitioned into a feed pipe and a discharge pipe; the feed pipe and the discharge pipe are coaxially and hermetically connected to both sides of the steam box; the conveying belt is arranged in the conveying pipeline and the steam box in a penetrating mode; a solvent storage box is arranged at the bottom of the steam box; a heater is arranged in the solvent storage box; a cooling coil is arranged on the top of the inner wall of the steam box; cooling pipes are arranged on connecting segments between the feed pipe and the discharge pipe and the steam box; solvent reflow pipes are arranged on the feed pipe and the discharge pipe respectively; decomposed gas collecting pipes are arranged on the solvent reflow pipes; the collecting pipes are used for converging into a gas treatment box. The gas-phase reflow soldering device has the beneficial effects that non-destructive welding of elements is realized through a gas phase reflowing way, and decomposed gas is introduced into the treatment box for treating, so that atmospheric pollution caused by decomposed gas is prevented.