Under the influence of flames with high temperature, high conductivity, solid particles and other factors, the electric field around UHVDC transmission lines increases significantly, which may cause trip of the transmission line. In this paper, taking Yun-Guang UHVDC transmission lines as the example, simulation studies are conducted to analyze the influence of charge density and particulates in forest fire on electric field under ±800 kV transmission line through Comsol software. Research shows that the maximum electric field strength increases significantly, up to 47 times higher than that under normal operating conditions when the flame charge density reaches 10¹⁴ m^-3 under stable combustion condition, the particles may cause distortion of the electric field, when the flame charge density reaches 10¹⁴ m^-3,the distortion value can reach 7.5 times of which under normal operating conditions, the distortion of the electric field caused by solid particles increases with the increase of the long axis and the decrease of the short axis.