Field analysis method is used to deduce the dispersion relation of rising-sun magnetron with sector cavities, which is proved correct by the high frequency field analysis software, and the influence of each structure parameter of the magnetron on the cutoff frequency of π mode and the mode isolation is investigated. The results show that the relative errors between the theoretical values and the simulation values of the dispersion relation are less than 3%, and the relative errors between the theoretical and simulation cutoff frequencies of π mode are less than 1%. Cutoff frequency of π mode is in direct proportion to the cathode radius Rc, anode radius Ra and big cavity angle 2θ1, but in inverse proportion to small cavity radius Rd0, big cavity radius Rd1 and small cavity angle 2θ0. However, these qualitative relationships are not entirely consistent with those of the same cavity magnetron. In radial orientation, the structure parameters, the influence of which on frequency is sorted in descending order, are as follows: anode radius, big cavity radius, small cavity radius and cathode radius. In angular orientation, the influence of big cavity angle on frequency is greater than that of small cavity angle. In addition, mode isolation γ is in direct proportion to big cavity radius Rd1, but in inverse proportion to cathode radius Rc, small cavity radius Rd0, and small cavity angle 2θ0, and it increases first and then decreases with the increase in anode radius Ra or big cavity angle 2θ1.