A　multi-layered　porous　finite　element　model　of　lithium-ion　battery　is　proposed　by　using　Voronoi　polygons.　The　time　domain　simulation　of　ultrasonic　transmission　characteristics　with　different　state　of　charge　(SOC)　are　carried　out,　and　the　variation　of　acoustic　parameters　versus　SOCs　is　explored.　Then,　in　the　experiment　research,　the　ultrasonic　transmission　signals　are　obtained　by　employing　piezoelectric　ceramic　transducers　during　the　dis-charging　step.　By　extracting　the　time　domain　characteristic　parameters,　it　is　discovered　that　the　amplitude　and　time-of-flight　(TOF)　have　a　strong　correlation　with　SOC,　the　slow　pressure-wave　(SPW)　velocities　of　the　exper-iments　correspond　well　with　the　simulation　results.　In　addition,　the　frequency　domain　analysis　shows　a　linear　link　between　the　amplitude　of　the　frequency　spectrum　and　SOC.　Moreover,　via　repeated　experiments,　it　is　found　that　the　ultrasonic　transmission　method　has　good　repeatability　in　probing　the　SOC,　and　the　SPW　velocities　ac-quired　by　experiments　can　almost　be　covered　by　95%　confidence　interval　formed　based　on　the　results　of　the　simulation.　Furthermore,　according　to　the　results　of　the　experiments,　a　gray　model　based　on　the　particle　swarm　optimization-based-simulated　annealing　(GM-PSO-SA)　is　established,　which　realized　the　prediction　of　the　SOC　under　the　condition　of　small　sample　data.　The　research　results　can　serve　as　a　reference　for　creating　a　compre-hensive　finite　element　model　of　the　multi-layered　porous　structure　of　lithium-ion　battery.　Meanwhile,　it　also　provides　a　detection　and　evaluation　tool　for　the　monitoring　of　the　SOC.