Abstract: Based on HF(Hartree-Fock) calculation method with 3-21G basis set, we discussed structural and dissociation characteristics of C₃H₄O gas molecules under different external fields (from -10.28 V·nm^-1 to 10.28 V·nm^-1). It is found that as the electric field increases along the direction of molecular conjugated single bond the total energy increases. The bond length of C-C double bond and C-C single bond decreases. The bond length of C-O double bond increases. The dipole moment decreases. Energy gap E_G increases. The infrared absorption peak has both red shift and blue shift at different frequencies and the intensity of IR also changes. The molecular dissociation performance is as follows: The potential energy barrier decreases with the increase of the external electric field. As the electric field reaches 25.71 V·nm^-1, the potential energy barrier almost disappears and the dissociation energy decreases gradually with the increase of the electric field, which indicating that the dissociation difficulty of C₃H₄O gas molecules under electric field decreases gradually. It provides reference for the study of dissociation characteristics of C₃H₄O gas molecules or mixtures containing C₃H₄O in external electric field.