The invention relates to a detection method and system for the one-phase open circuit of a rotating diode with a multi-phase angle joint brushless exciter. The method comprises the steps of after acquiring the exciting current entering the stator exciting winding of the exciter, filtering a direct current component and a phase frequency doubling component in the exciting current, thus acquiring acurrent simultaneously including odd and even harmonic waves; then dividing the current including the odd and even harmonic waves into two paths, thus acquiring a first current and a second current; delaying the second current for reference time to acquire a first delayed exciting current; subtracting the first delayed exciting current from the first current to acquire the current including the odd harmonic waves; and performing one-phase open circuit detection on the rotating diode on the current simultaneously including the odd and even harmonic waves and the current including the odd harmonic waves. According to the method, the accurate judgment on the fault can be achieved, the additional device is not needed either, the motor structure does not need to be modified, the technical difficulty and cost are reduced, and the detection reliability is high.