Abstract: A multi-channel tunable diode laser absorptionspectroscopy (TDLAS) system was constructed to measure flow parameters in adirect-connected scramjet test facility fueled with ethylene. Two fiberscoupled distributed feedback (DFB) lasers with narrow line width were usedto probe two H_2O absorption featuresby using direct absorptiontime-division-multiplexing (TDM) strategy at a 4kHz scan rate. Flowparameters were measured, which included the distribution of temperature,water vapor concentration and velocity at the exit cross section of thecombustor, the distribution of temperature and water vapor concentration inthe cross section near the cavity. Combustion efficiency was obtained byusing the water vapor partial pressure distribution and the wall staticpressure. Mach number distribution was deduced from the temperature andvelocity parameters distributions at the exit cross section of thecombustor, and the distributions of temperature and water vaporconcentration in the cross section near the cavity were used to analyzecombustion characteristics in the combustor.