An　under-gate　field　emission　display　(FED)　with　a　concave　cathode　is　proposed.　Ansys　software　is　used　to　simulate　the　electric　field　distribution　and　the　focus　effect　of　electron　beams.　The　curvature　radius　of　a　concave　cathode　which　affects　the　self-focus　is　investigated.　The　results　demonstrate　that　the　concave　cathode　focuses　electron　beams　which　emit　from　cathode　obviously.　As　the　curvature　radius　of　a　concave　cathode　decreases,　the　focus　effect　is　enhanced　and　the　radius　of　spots　on　the　anode　decreases　too.　A　10　cm　×　10　cm　FED　with　a　good　self-focus　effect　is　successfully　prepared　using　screen　printing.　The　field　emission　image　shows　that　the　structure　can　decrease　the　size　of　spots　and　improve　the　resolution.　The　anode　current　is　well　modulated　by　a　gate　voltage　of　100-250　V　under　an　applied　anode　voltage　of　600　V.