A flat laminar non-adiabatic flame in premixed gas mixture is considered. Stability of gas mixture burning with instantaneous and periodic pertubations is theoretically studied. Zero-dimensional linearized models (dynamic systems of the second and third order) are studied analytically, the non-linear zero-dimensional and initial one-dimensional systems are solved numerically. Parameter regions with nonunique and auto-oscillatory combustion regimes are determined. The influence of lateral heal removal, radiation, burning temperature, reaction kinetics, injection rate, etc. on the non-unique and auto-oscillatory regime, character and number of critical conditions is studied. The performance of forced oscillations and the resonance phenomena are found.