Indoor air quality affects human health, with CH2O, NH3 and Benzene being the three most common indoor toxic gases. In this work, we investigated the adsorption of transition metal (Fe, Zr, Ta, Tc) doped boron nitride nanosheets (BNNSs) for three indoor toxic gases based on density functional theory (DFT). Through a series of analyses after simulation, the results show that the adsorption of pristine BNNSs for the three toxic gases is low, whereas the adsorption of transition metal doped BNNSs for all the three gases are significantly enhanced. Among them, Ta-BNNSs is the structure with a large change in band gap after adsorption of CH2O and Benzene. For NH3, the band gap change after adsorption of Tc-BNNSs is the largest. We have analyzed the recovery time of these three adsorption systems at 298 K, 398 K and 498 K. The results showed that the recovery time of Ta-BNNSs for adsorption of CH2O or Benzene at all three temperatures was large, while the recovery time of Tc-BNNSs at 498 K was small. Thus Tc-BNNSs are a potentially recyclable NH3 sensor material. Finally, the relative adsorption energy analyses showed that Fe-BNNSs had large adsorption energies for all three toxic gases at room temperature and the desorption temperatures were all around 700 K. Therefore, Fe-BNNSs are promising as a recyclable adsorbent material for the three toxic gases.