Annual　cycles　in　the　geocenter　motion　time　series　are　primarily　driven　by　mass　changes　in　the　Earth’s　hydrologic　system,　which　includes　land　hydrology,　atmosphere,　and　oceans.　Seasonal　variations　of　the　geocenter　motion　have　been　reliably　determined　according　to　Sun　et　al.　(J　Geophys　Res　Solid　Earth　121(11):8352–8370,　2016)　by　combining　the　Gravity　Recovery　And　Climate　Experiment　(GRACE)　data　with　an　ocean　model　output.　In　this　study,　we　reconstructed　the　observed　seasonal　geocenter　motion　with　geophysical　model　predictions　of　mass　variations　in　the　polar　ice　sheets,　continental　glaciers,　terrestrial　water　storage　(TWS),　and　atmosphere　and　dynamic　ocean　(AO).　The　reconstructed　geocenter　motion　time　series　is　shown　to　be　in　close　agreement　with　the　solution　based　on　GRACE　data　supporting　with　an　ocean　bottom　pressure　model.　Over　85%　of　the　observed　geocenter　motion　time　series,　variance　can　be　explained　by　the　reconstructed　solution,　which　allows　a　further　investigation　of　the　driving　mechanisms.　We　then　demonstrated　that　AO　component　accounts　for　54,　62,　and　25%　of　the　observed　geocenter　motion　variances　in　the　X,　Y,　and　Z　directions,　respectively.　The　TWS　component　alone　explains　42,　32,　and　39%　of　the　observed　variances.　The　net　mass　changes　over　oceans　together　with　self-attraction　and　loading　effects　also　contribute　significantly　(about　30%)　to　the　seasonal　geocenter　motion　in　the　X　and　Z　directions.　Other　contributing　sources,　on　the　other　hand,　have　marginal　(less　than　10%)　impact　on　the　seasonal　variations　but　introduce　a　linear　trend　in　the　time　series.　©　2018,　Institute　of　Geophysics,　Polish　Academy　of　Sciences　&　Polish　Academy　of　Sciences.