Abstract: In order to understand the influence of injector indentation length and combustion chamber length on high frequency combustion instability of oxygen/kerosene rocket engine, the combustion experiment of single-element model engine was designed and carried out. The gas-liquid coaxial centrifugal single-element was used in the experiment. In order to test the combustion stability, the length of the combustion chamber and that of the injector were used as experimental variables, and the data were collected by high frequency pressure sensor, using the central supply of oxygen and the axial rotation of liquid kerosene through the tangential hole into the injector. Based on the pressure signal, the experimental results, especially the longitudinal high frequency combustion instability, are studied in detail. The results show that:under the conditions studied in this paper, with the increase of the indentation length, the longitudinal high frequency combustion instability is damped, but the longitudinal high frequency combustion instability is not eliminated. The length of combustion chamber is between 516mm and 356mm. The effect of the injector indentation length on the combustion stability is negligible. With the increase of combustion chamber length, the first order longitudinal acoustic frequency decreases gradually. These phenomena are due to the phase difference between the combustion pressure oscillation and the acoustic wave. In addition, the influence of the combustion chamber length on longitudinal high frequency combustion instability is more obvious than that of the indentation length.