The invention discloses a screw for fixing a resonant bar, a filter adopting the screw and communication equipment adopting the cavity filter; the screw is provided with a bar part which is at least locally provided with a thread; one end of the bar part is a screw head; a transition area is formed between the screw head and the bar part; a circular groove is arranged around the transition area with the bar part as the center; the transition area is arranged in the groove; the depth of the groove is more than the height of the transition area; and when the resonant bar is fixed, the top surface of the groove presses the bottom of the resonant bar, so that the resonant bar is fixed. The cavity filter adopts the screw, the transition area of the screw is arranged in the groove, so that the transition area does not press the bottom surface of the resonant bar, the resonant bar can be very well fixed under the condition that the screw has equal stress, and the phenomena that the resonant bar deforms and the performance of the filter is affected due to the transition area do not exist. The communication equipment adopts the cavity filter, so that the filtering performance can be very well realized.