To examine the pressure effect on burning rate, flame height and axial temperature distribution of diffusion fires, experimental measurement and theoretical analysis on circular n-Heptane fires with serial sizes were conducted at two altitudes, i.e. 100,8 kPa (in a sea-level city Hefei) and 64.3 kPa (in a Tibetan city Lhasa). From the results, the mean burning rate at quasi-steady stage and boiling stage consistently implied that the exponent alpha (m '' (D) over tilde P-x) varies for different heat transfer domination stages, i.e. alpha <= 0 for conductive stage and alpha = 2/3 for convective stage. Analysis shows that the flame height, the axial flame and plume temperatures are all well correlated with the dimensionless heat release rate Q similar to Q/(PD5/2), with the correlation coefficients derived from the current low-pressure measurements. Analysis shows that the flame height and the plume temperature increase with the pressure rise as a power function of pressure for the same pool size. (C) 2013 Elsevier Ltd. All rights reserved.