Abstract: Gaseous ethylene ignition experiments were carried out on directly-connected pulse combustion facility.The stagnation temperature and the Mach number at the isolator entrance were 935K and 2 respectively,which simulated the flight with Mach number 4.Ethylene was ig-nited successfully and stable combustion was maintained by employing torch igniter and pilot hy-drogen.Wall pressure measurement,high speed imaging and numerical simulation were em-ployed to analyze the ignition and flame propagation processes.The results indicate that:(1)the recirculation zone in the cavity avails ignition,while the shear layer and the rear of the cavity are the main regions for stable combustion;(2)after ignition,the density of the fuel and oxidizer is the key factor to stable combustion,and oxidizer that continually entering the shear layer and rear of cavity supports the stable combustion;(3 )combustion downstream of the cavity pro-motes the pressure level in the combustor,and the unstable combustion there causes pressure os-cillation.The high velocity and variation of oxygen content are the two main factors including un-stable combustion downstream of the cavity.