Abstract: A new synthetic flight stability criterion of aircraft at high angles-of-attack isdeveloped in thispaper by analyzing the operator matrix of 5 degrce-of-freedom motion equations of aircraft after a brief introduction and interpretation of several simplified criteria concerned with the flight stability of aircraft, such as dynamic directional stability parameter mBy.dyn.departure predicting criterion Phillips parameter LCDP which is closely involved with the stability of aireraft at high angle-of att ack .The new eritrion synthesizes all the above simplified criteria, and reveals the relationships among them.