Based on priciples of PAS and TDLAS, relevance between them was dicussed, while the relationships of PAS and TDLAS signal with pressure were derived. A contrast device for making PAS and TDLAS gas detection simultaneously was designed and constructed to test different pressure and provide a reference for the gas measurement technology selection under different pressure conditions. Experimental studies show that: as the pressure rises, PAS and TDLAS signals become larger, and limit detection sensitivity are improved; with the rising pressure, conversion efficiency from energy absorbed by gas to PAS signals becomes low; at low pressure condiction, PAS is a better choice.