Numerical and experimental study on bearing stiffness,bearing capacity and critical speed characteristics of a 30 kW micro gas turbine aerostatic bearing was carried out.There will be critical characteristics caused by the bearing gas film before the rotor reaches the firstorder bending critical speed of a micro gas turbine supported by gas bearing.This phenomenon was analyzed by numerical simulation and experimental verification.The compressible Reynolds equation was discretized and solved by numerical iteration method to obtain the pressure distribution and the gas film stiffness of the bearing.The modal characteristics and critical speed of the rotorbearing system was studied by finite element method.Based on the micro gas turbine test bench supported by gas bearing,the critical speed of the gas film of the shaft system was obtained by the vibration test and analysis methods such as timedomain vibration signal and unbalanced response curve.The results show that the dynamic pressure effect of the studied static pressure gas bearing can be neglected compared with the static pressure effect within the the rotational speed of 30 000 r/min.The bearing film rigidity is increased with the increasing of eccentricity.However,when the eccentricity exceeds 08,the stiffness of the gas film is decreased due to the ‘static instability zone’.Both numerical simulations and experiments proves that the critical characteristics of the cone motion caused by the stiffness of the gas film appear near the speed of 6 000 r/min and 9 000 r/min.