Abstract: The effects of various coupling factors on resonant frequency and mode separation of magnetrons should be investigated to improve the stability of the magnetrons. The resonant frequency and the mode separation of the unstrapped magnetron with capacitance and inductance coupling are derived using equivalent circuit method. Besides, the change of resonant frequency and the effects of capacitance and inductance coupling on mode separation are also numerically calculated. Moreover, the resonant frequencies of magnetrons are simulated by CST-MWS, which are compared with theoretical results. Theoretical analysis and computer simulations show that as the mode number increases, the resonant frequency of unstrapped magnetron induced by the capacitance coupling increases, while the inductance coupling is opposite. The two couplings can both enlarge the mode separation by opposite methods. The mode spectrum of unstrapped magnetron with capacitance and inductance coupling depends on the dominant coupling factor.