Abstract: Previous studies show that HFO-1234ze(E) has good insulating properties and environmental protection properties, which has the potential to be used as an insulating medium in electrical equipment. The gas insulating medium is worked in the equipment under an external electric field and there is no research on the influence of the external electric field on the gas properties of HFO–1234ze(E). Therefore, in this paper, the influence law of electric field on the molecular structure and property parameters of HFO–1234ze(E) is obtained through theoretical calculations. Then, the changes in the microscopic properties of HFO–1234ze(E) under different electric fields are analyzed. Finally, the essence of its good insulating properties is revealed. The calculation results show that there are obvious changes in the other bond lengths except for the C—H bonds in HFO–1234ze(E). In SF₆, there is only the chemical bond S-F along the electric field changes. The energy gap of HFO–1234ze(E) decreases with the increase of the external electric field, and the electronic transition is more likely to occur and the chemical stability of the molecular decreases. The charge density near the C=C double bond is large, which has a strong chemical reaction. At the same time, the energy gap of HFO–1234ze(E) is generally smaller than that of SF₆, indicating that its molecular structure and chemical stability are slightly weaker than those of SF₆. The changes in the structure of molecules lead to changes in its properties, and the dielectric strength of gas is closely related to the polarizability and ionization energy of molecules. In this paper, the ionization energy is slightly lower than that of SF₆ and the polarizability of HFO–1234ze(E) is significantly higher than that of SF₆ under different applied electric fields. At the same time, according to the power frequency test results, the breakdown voltage of HFO–1234ze(E) is 0.78~0.89 of that of SF₆ with the gas pressure in 0.1~0.3 MPa, which has good insulating properties.