In-situ conversion of H2S to valuable chem. products is a desirable route to remove H2S for resource utilization in modern industry.Herein, a series of bi-quaternary ammonium ionic liquids (BAILs) have been developed and played dual roles as both absorbent and catalyst for absorption and transformation of H2S into thiols or thioether with high conversion under mild conditions, accomplishing the heterogeneous separation of product and catalyst without introducing the third component.It was found that N,N,N,N5,N5,N5-hexapropylpentyl-1,5-diaminopropionate ([C5(N333)2][Pro]2) exhibited outstanding absorption performance with the H2S capacity reaching 1.34 mol/mol ILs at 303.2 K and 1.0 bar.The various α,β-unsaturated carboxylate esters were applied to explore product selectivity for monomer or dimer by temperature and the partial pressure of H2S.Conversion of substrates and selectivity of dimer were all over 99% within 1 h at 40°C, 0.1 bar with only 10 mol% [C5(N333)2][Pro]2 loading due to the extraordinary catalytic activity.The reaction catalyzed by [C5(N333)2][Pro]2 can obtain high-purity monomer products for 1.0 h at 0°C and 7.0 bar.Furthermore, [C5(N333)2][Pro]2 kept effective catalytic activity after five recycle.This work provides an in-situ strategy to transform H2S into value-added products without traditional desorption procedures, which enriches the choice for treatment of H2S under different low partial pressure scale.