The ignition reliability of combustor is related to the safety of the whole machine, especially the high-altitude ignition and combustion stability, which are the common requirements of the combustor. In this paper, the simulated altitude test facility was introduced. And the ignition performances of a linear combustor with five burners were carried out under the simulated altitude of 0–8 km, including the ignition boundary and flame propagation between burners. The process of flame propagation was recorded by a high-speed camera. The results indicate that the fuel-air ratio increases with the increase of altitude at the same pressure drop, and it decreases with the increase of pressure drop. For the period of ignition delay, the evaporation of droplets and the chemical delay process are mainly affected with the increase of altitude. At the altitude of 6 km to 8 km, flame propagates from burner to burner in an axial pattern, and the influence of altitude on flame propagation is mainly manifested in ignition delay and initial flame propagation. The key to improve the reliability of high-altitude ignition is to improve the fuel atomization and evaporation characteristics. The contribution of this article is to explore the mechanism of altitude on ignition characteristics and propose two methods to improve the high-altitude ignition characteristics.