In　this　study,　the　problem　of　adaptive　modulation　and　frame　length　(AMFL)　is　investigated　in　long-term　evolution　for　railway　(LTE-R)　communication　system.　By　considering　the　effect　of　frame　length,　a　novel　AMFL　strategy　based　on　Moore　state　machine　(MSM)　is　proposed.　The　influence　of　the　frame　length　on　the　goodput　is　discussed　by　theoretical　analysis　and　simulation　evaluation.　According　to　modulation　and　frame　length　schemes　(MFLSs)　adopted　in　LTE-R　system,　the　finite　state　set　of　the　MSM　is　designed.　For　different　MFLSs,　the　frame　error　rate　(FER)　and　signal-to-noise　ratio　(SNR)　curve　is　obtained.　By　giving　a　target　FER,　the　SNR　thresholds　corresponding　to　different　MFLSs　are　achieved.　From　the　perspectives　of　modulation　priority　and　frame　length　priority,　two　different　AMFL-MSMs　are　designed　to　change　MFLSs　dynamically.　Simulation　results　show　that　the　proposed　two　AMFL-MSMs　have　more　stable　goodput　than　the　common　modulation　schemes　and　less　symbol　energy　consumption　than　the　high-order　modulation　scheme.　In　addition,　the　AMFL-MSM　with　modulation　priority　has　better　performance　than　the　AMFL-MSM　with　frame　length　priority　in　terms　of　goodput　stability.