Experiments were conducted on the insulation materials of EPS and XPS in a small-scale flame spread experimental bench in the Tibetan plateau area of Lhasa (with an altitude of 3658 m) and the plain area of Hefei (with an altitude of 50 m), respectively. The detailed flame structure including flame angle, flame length and maximum length of pool fire over EPS and XPS with thicknesses of 2 cm, 3 cm, 4 cm and 5 cm inclined at the angles of 30 to 30 was investigated. It is found that for the same thickness of EPS and XPS inclined at the same angle, the flame length is longer and the flame angle is smaller in Hefei than those in Lhasa in the wall fire zone, which is in good agreement with the predictions. The preheating length delta(f) is correspondingly longer in plain due to smaller flame angle and longer flame length and the flame heat flux (q '')over dot increases with air pressure, which make the flame convective and radiative heat (q '')over dot (2)delta(f) larger leading to promote flame spread. For the horizontal flame spread over EPS and XPS, the maximum length of pool fire is significantly smaller than that in other incline angles in Lhasa, which can be attributed to the smallest heat transfer to the residue pool fire zone during flame spread making PS in the residue pool fire zone extinguish more easily. (C) 2015 Elsevier Ltd. All rights reserved.