Abstract: ADN monopropellant green space propulsion is perceived as a focus of the space propulsion research worldwide. Experimental study is in urgent requirement for understanding the combustion process in the ADN based thruster and for quantitative evaluation and optimization of the combustion stability and the thruster performance. In this paper, experiments were conducted to measure the concentration of the key intermediate products (CO, N₂O) and the temperature of the combustion gas flow based on the mid-infrared quantum cascade laser absorption spectroscopy (QCLAS). Two main ignition modes of the 1 N ADN based thruster are studied: the steady-state firing and the pulse-mode firing over the injection pressure of 0.5~1.2MPa bar with catalytic bed length of 19 mm, corresponding to a current thruster prototype. It is found in the steady-state firing experiments that the whole process can be divided into the catalytic decomposition stage and the combustion stage, and the combustion kinetics mechanism of the monopropellant is experimentally demonstrated. Experiments for the pulse-mode firing show the variance of the measured multispecies concentration and temperature in consistence with the pulse trains, verifying the good performance of the thruster pulse-mode firing operation.