Numerical computations on vapor flow and non-absorbable gas diffusion in the evaporator/absorber are performed in order to research the extraction method of non-absorbable gas. Non-absorbable gas behavior was tried to control by using an immersed plate and an extraction. From the results, it was found that both the immersed plate and the extraction can prevent from the performance decrease of the absorber. Non-absorbable gas tended to stay in the low vapor velocity region, because non-absorbable gas is rolled up into the low velocity region. Non-absorbable gas diffused from the low velocity region, when the vapor velocity entirely becomes lower because of the absorber performance decreases. In order to extract non-absorbable gas effectively, the extraction vent should be mounted near the position where non-absorbable gas was concentrated.