In　order　to　further　increase　the　power　density　for　axial-piston　pump,　the　quantitative　formulas　were　derived　and　the　most　important　factors　were　studied.　One　factor　was　the　amount　of　volumetric　displacement　of　pump　per　revolution　divided　by　the　spatial　volume　of　pump,　and　the　analysis　indicated　that　it　was　determined　by　swash-plate　angle　and　piston　pitch-radius,　and　60%　increase　of　it　could　be　obtained　by　using　an　inverted　piston-slipper　design.　The　other　factor　was　the　maximal　speed　which　was　determined　by　the　self-priming　ability　(SPA)　of　pump.　The　analysis　result　showed　that　the　SPA　was　affected　by　resistance　caused　by　viscous　resistance　and　forced　vortex,　and　the　ability　dropped　with　the　rotating　speed　increasing,　which　was　the　defect　of　current　structure　of　cylinder　block.　In　order　to　overcome　the　defect,　a　new　structure　of　cylinder　block　with　bidirectional　inclined　cylinder　block　hole　was　presented,　and　the　results　of　simulation　demonstrated　that　SPA　of　axial-piston　pump　was　increased　by　45.4%.　Finally,　to　meet　the　requirement　of　large　displacement　pump,　a　symmetrical　X　shape　axial-piston　pump　was　proposed　and　its　power　density　was　verified　theoretically.　The　analysis　result　showed　that　the　power　density　was　increased　by　43%　compared　with　a　double-pump.　©,　2015,　Chinese　Society　of　Agricultural　Machinery.　All　right　reserved.