The invention relates to a minimum Q value self-excitation tuning system and method. The system comprises a self-excitation module, a minimum Q value control module, a motor driving module, a first amplifier, a shunt and a resonant cavity. One end of the shunt is connected with the cavity pressure signal sampling end of the resonant cavity, and the other end of the shunt is connected with the self-excitation module and the minimum Q value control module; the output end of the self-excitation module is connected with the first amplifier and the second input end of the minimum Q value control module; the output end of the first amplifier A1 is connected with the signal input end of the resonant cavity; the output end of the minimum Q value control module is connected with the input end of the motor driving module to determine whether the tuning system is in a resonance state or not, if not, the driving signals are transmitted to the motor driving module; and the output end of the motor driving module is connected with the motor control end of the resonant cavity to perform automatic tuning for the resonant cavity. The minimum Q value self-excitation tuning system and method can be widely applied into an accelerator coordination system.