A series of experiments of the upward flame spread over polyethylene-coated wire with copper core were conducted in a newly designed high-pressure chamber to study the effects of the wire inclination angles and ambient pressures. The angle of inclination changed from 0 degrees to 75 degrees and the pressure ranged from 100 kPa to 400 kPa. The results show that the flame spread rate increases with the inclination angle and the pressure. The characteristic lengths including the flame length, the flame base width and the pyrolysis length present an increasing trend with increasing inclination angles, while the elevated pressure results in that the flame length and flame base width decreases and the pyrolysis length increases. Moreover, a simplified heat transfer analysis model considering the convective, radiant and conductive heat feedback is proposed to discuss the flame spread mechanism. Based on the theoretical analysis, convective heat transfer from flame and conductive heat transfer from wire core play significant roles in heating the unburned insulation with the increase of inclination angles. For the cases with higher pressure, the heat transfer from flame including heat convection and heat conduction plays a dominant role in increasing the heat feedback to the unburned wire. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.