The invention discloses a circuit breaker non full phase judging method based on a two-side voltage fundamental wave amplitude change rate. A protection device is used for measuring three-phase voltage and open delta voltage at the left side and the right side of the circuit breaker; fundamental wave amplitudes of the three-phase voltage and the open delta voltage at the left side and the right side of the circuit breaker and the change rate of the fundamental wave amplitudes of the open delta voltage at the left side and the right side are calculated respectively; when the fundamental wave amplitudes of the three-phase voltage at the left side and the right side are both larger than eta% of rated voltage, the fundamental wave amplitudes of the open delta voltage at the two sides are both larger than a fundamental wave amplitude threshold, and the fundamental wave amplitude change rate of the open delta voltage at either side of the left side and the right side is larger than a change rate fixed value threshold at the corresponding side, non full phase of the circuit breaker is judged, and alarming or tripping is carried out after a short time delay t.