A kind of FBAR filter chip for S band application is developed successfully with fully independent design and process technique . The filter is composed of ladder circuit，it is simulated and optimized using one dimensional Mason model. In the technical realization, the device has air gap structure. Both the deposition technology of AlN piezoelectric film with high c axis oriented and precision air gap are broken through. The fabricated 4 pole FBAR filter has the center frequency of 2 340 MHz, the 3 dB bandwidth of 25 MHz, the insertion loss at center frequency of 3.8 dB, the shape factor of 2.24∶1,and both the input and output impedance of 50 Ω. The chip size is only 1 mm×1 mm×0.3 mm. The above performance is compared with dielectric filter having the same frequency and bandwidth. The volume of FBAR filter is reduced by several permillage, and the shape factor outgoes the dielectric filter obviously.