Based on typical truck’s climbing performance in real driving test, the truck’s speeddistance curves on different gradients at different altitudes were built. The results show that the truck’s climbing speed on slope decreases more rapidly and the stable speed on slope is lower at a higher altitude when the altitude is between 3 000 m and 5 000 m. Then, the maximal gradient of highway with design speed 100, 80 and 60 km?h-1 in highaltitude area was proposed. Compared with that specified at the same design speed in general area in existing standard, it decreases by 1%~2%.