This　paper　proposes　a　kind　of　broadband　metasurfaces　that　can　independently　and　finely　control　the　amplitudes　and　phases　with　a　high　efficiency　for　both　reflection　and　transmission　modes.　A　Fabry-Perot　(FP)　cavity　and　a　metallic　dual-split　ring　(DSR)　polarizer　are　combined　to　construct　each　element　of　the　metasuface　that　has　an　ultrathin　and　planar　structure.　The　forward　cross-polarization　transmission　and　backward　co-polarization　reflection　can　be　switched　easily　by　varying　the　DSR　polarizer.　It　can　offer　the　arbitrary　combination　of　amplitudes　within　[0,　1]　and　phases　within　the　range　of　[0,　360°]　for　both　transmission　and　reflection　modes.　The　proposed　metasurface　was　applied　to　design　high-gain　low-sidelobe　transmitarray　antenna　(TA)　and　reflectarray　antenna　(RA).　Comparisons　between　metasurfaces　based　on　the　phase　control　only　and　those　based　on　the　control　of　both　phase　and　amplitude　are　studied.　Numerical　simulation　results　verify　the　described　superior　performance.　©　2022　IEEE.