Abstract: Based on density functional theory, the effects of the electronic structure of monolayer BiSbTe₃ under external electric field and strain have been systematically studied. As the electric field increases from −0.4 V/Å to 0.4 V/Å, the band structure and band gap of monolayer BiSbTe₃ nanofilm remained almost unchanged under the external electric field, which is attributed to the shielding effect. As the biaxial strain increases from −6% to 6%, the band gap of monolayer BiSbTe₃ nanofilm gradually decreases. Near the Fermi level, the conduction band becomes flatter. In contrast, compressive strain induces the opposite changes. This study can provide a theoretical reference for regulating the electronic structure and thermoelectric properties of two-dimensional thermoelectric materials by external electric field and strain.