Abstract: Monolayer InSe has excellent thermoelectric properties due to its large Seebeck coefficient and electrical conductivity. Using first-principles calculations, the structure, electronic structure and charge transfer of monolayer InSe under the external electric field were systematically studied. The results show that when the electric field strength is in the range of 0 - 0.6 V/Å, the conduction band and the valence band near the Fermi level are insensitive to the external electric field, and the band gap hardly changes with the external electric field. This is mainly due to the transfer of free electrons around the upper and lower Se-In atomic layers after the application of an external electric field, which makes the monolayer InSe shield the external electric field. Under the shielding effect, the structure of the monolayer InSe and its internal chemical bonds are less affected by the external electric field, which makes the energy band of the monolayer InSe insensitive to the external electric field. This study can provide a theoretical reference for the regulation mechanism of external electric field on the electronic structure and physical properties of two-dimensional materials.