A unified numerical analysis was conducted to investigate the inlet buzz and combustion oscillation in an axisymmetric ramjet engine. The inlet buzz phenomenon in the subcritical operation arises large pressure oscillation, combustion instability, engine surge, and thrust loss, etc. The physical model of concern includes the entire engine flow path, extending from the leading edge of the inlet center-body through the exhaust nozzle. The theoretical formulation is based on the Farve-averaged conservation equations of mass, momentum, energy, and species concentration, and accommodates finite-rate chemical kinetics and variable thermo-physical properties. Turbulence closure is achieved using the combined model of a low-Reynolds number k-ε two-equation model and Sarkar's compressible turbulence model. The detail flow structures such as buzz shock train, shock/boundary layer interaction, and flame fluctuation are observed. Both the driving source to the inlet buzz and buzz effects on both flow and flame evolutions are studied.