Abstract: Magnetron structure and quasi magnetron structure (no cathode) are the basic elements of magnetron with diffraction output (MDO). It is the groundwork for studying the mode conversion and transmission in MDO to analyze the dispersion relation of the two types of magnetron structures. Based on the field match method, the dispersion relation of quasimagnetron is obtained, and then the relation between the wave-numbers at π mode resonant points and the geometry parameters in six cavity and two-cavity magnetron and quasimagnetron are quantitatively analyzed by numerical computation respectively. For magnetron structure, when the distance between cathode and anode is unchanged, π mode wave numbers increase with decreasing the radius of resonant cavity; when the radius of resonant cavity i