A flexible circuit board includes a wiring layer, two photosensitive resin layers, and two electromagnetic interference shielding layers. The wiring layer includes at least one signal line, two ground lines and at least two gaps. Each gap includes two opening portions. The two photosensitive resin layers cover the signal line and the opening portions, and are connected to each end of each ground line. Each electromagnetic interference shielding layer covers one photosensitive resin layer away from the signal line, portions of the two ground lines not connected to the photosensitive resin layer, and portions of the gaps not covered by the two photosensitive resin layers, thereby causing the portions of each gap not covered by the two photosensitive resin layers to define a receiving chamber. Each end of each receiving chamber communicates with one opening portion of the corresponding gap to define a cavity.