To investigate the fire behavior under low pressure, four configurations of cardboard box fires were comparatively tested in a sea-level city, Hefei, and a high-altitude city, Lhasa. During each test, mass burning rate, total heat release rate, multipoint flame temperature, and radiative heat flux were measured. From the experimental data, some specific fire behavior was observed that (1) the mass burning rate divided by fire base dimension can be correlated against the production of pressure-squared times length-cubed (P²L³) to the power of 0.31, (2) the heat of combustion is lower in Lhasa probably due to the incomplete solid pyrolysis limited by oxygen, (3) the dimensionless plume temperature is correlated against the dimensionless flame height with a pressure term to the power of −2.0, and (4) the relative flame temperature estimated from the radiative heat flux indicated that the overall flame temperature is higher in Lhasa.