Abstract: The eigenequation of coaxial waveguide with inner and outer slotted structure is derived using the fields matching method, and the outer slotted cylindrical waveguide eigenequation is derived as well. Numerical simulation is conducted on the propagation characteristics of 2π mode in the inner and outer slotted structure and the outer slotted structure. The relationship between slot depths and eigenvalues of both structures is discussed, as well as the relationship between frequency and radiuses in the former structure. The results reveal that, the eigenvalue of inner and outer slotted waveguide increases with deeper inner slot, and decreases with deeper outer slot. The waveguide frequency is almost independent of inner radiuses, but is significantly affected by outer radiuses.