Emulsified　cement　asphalt　mortar　(CA　mortar)　seam　is　a　common　defect　in　the　running　of　China　Railway　Track　System　II　(CRTS　II)　slab　ballastless　track,　and　this　error　affects　safety　during　high-speed　driving.　The　influence　of　CA　mortar　seam　on　track　structural　performance　is　analyzed　on　account　of　the　temperature　and　static　loads　of　the　train　in　previous　studies.　To　explore　the　influence　law　of　CA　mortar　seam　on　the　safety　of　vehicle-CRTS　II　slab　ballastless　track　system　under　dynamic　load,　a　nonlinear　finite　element　model　for　the　vehicle-CRTS　II　slab　ballastless　track-subgrade　system　under　track　irregularity　is　proposed　in　this　study.　The　finite　element　calculation　models　for　vehicle-CRTS　II　slab　ballastless　track　and　seam　were　respectively　established　on　the　basis　of　the　coupling　dynamics　of　wheel　rail　system　and　finite　element　method.　MATLAB　program　was　also　compiled　to　simulate　the　track　irregularity　of　medium-long　wave　and　short　wave.　The　system　model　and　track　irregularity　were　then　both　applied　to　ABAQUS　numerical　analysis.　The　influence　of　CA　mortar　seam　on　the　system　dynamic　characteristics　with　different　train　speeds,　seam　lengths,　and　heights　was　studied.　Results　show　that　when　the　train　speed　is　300　km/h,　the　length　of　seam　is　1.2　m　and　the　height　of　seam　is　3　mm.　The　seam　exerts　minimal　effect　on　the　dynamic　characteristics　of　the　vehicle　system,　which　significantly　influences　the　vertical　acceleration　of　track　slab,　with　an　increase　of　144.3%;　the　higher　the　train　speed,　the　greater　the　dynamic　response　of　vehicle　and　track　system,　and　the　greater　the　influence　of　seam　on　driving　safety;　the　vehicle　dynamic　response　of　rail　and　track　slab　increases　with　the　increase　of　the　length　of　seam,　which　is　significant　when　the　seam　length　is　more　than　1.2　m.　When　the　seam　height　tends　to　1　mm,　the　dynamic　response　of　rail　and　track　slab　increases　significantly　and　then　stabilizes.　This　study　provides　theoretical　reference　for　the　safety　assessment　of　slab　ballastless　track.　©　2017　Eastern　Macedonia　and　Thrace　Institute　of　Technology.