It is important for life safety and scientific research to design new sensing materials for detecting CO, CH 4 and CO 2 from environment. We theoretically designed a new Cr-doped graphene-like hexagonal borophene (CrB 6 ) as potential sensor material for these gases. Carrying out firstprinciples density-functional calculations, we calculated the adsorption energy, band structure, adsorption distance, charge transfer, charge density difference, density of states and partial density of states of CO, CH 4 and CO 2 gas molecules absorbed on CrB 6 monolayer. The calculated results show that the adsorption behavior of CO is different from those of CH 4 and CO 2 . CO adsorbed on CrB 6 monolayer prefers chemisorption while CH 4 and CO 2 adsorbed on CrB 6 monolayer prefers physisorption. As a result, the different adsorption behaviors have significant influence on the band structures and density of states of CrB 6 monolayer. We hope that our results can help experimentalists synthesize better sensor materials based on hexagonal borophene.