This paper introduced the principle and design method of a narrowband band-pass cavity filter. The parasitic passband was moved away from the passband by increasing the loading capacitance. The resonator with dumbbell-shaped cross-bar was designed to form the zero point of the voltage standing wave at the junction of the resonator in order to suppress the parasitic passband of the filter and to implement a band-pass filter with wide attenuation band. Finally, a band-pass filter with a center frequency of 2.45 GHz and bandwidth of 4.08% was designed using the simulation software CST. The simulation results showed that the designed filter had high out-of-band rejection, wide attenuation band and good performance of voltage standing wave ratio in the passband, which meet the design specifications.