We performed the adsorption of NO2 on transition metal (TM) doped InN monolayer by using density functional theory (DFT). Firstly, adsorption of four kinds of TM atom (Pd, Pt, Ag, Au) on pristine InN monolayer was explored including four different adsorption sites (T-In, T-N, BIn-N and H). Then, for NO2 adsorption, by calculating adsorption energy, adsorption distance, charge transfer, magnetic moment and density of states, the chemical interactions between NO2 and TM doped InN monolayer (TM-InN) were discussed. We have gotten the following results: (1) Pd, Pt, Ag, Au atoms are all likely to be adsorbed on T-N site with exothermal process; (2) Pt and Au gain electrons while Pd and Ag lost electrons and Ag and Au can introduce magnetic moment to InN monolayer; (3) NO2 can be chemi-adsorbed on TM atom modified InN monolayer due to the considerable adsorption energy and charge transfer; (4) NO2 molecule orbitals experience significant changes after adsorption. This study can provide prospects and possible application value for TM-InN to be a potential material to adsorb and detect NO2.