Abstract: This paper presents computation and analysis of tangential mode of high frequency combustion instability in FY-20 liquid propellant rocket engine by means of the annular instability model. The results show that the tangential mode of high frequency unstable conbustion does not occur in the engine, that coincides with the experimental results. Concrete steps and some effective measures for improving the liquid propellant rocket engine which is weak in the tangential mode of high frequency stability are also described in the paper.