A　compact　and　broadband　polarization　beam　splitter　(PBS)　based　on　silicon　(Si)　nitride　(SiN)-on-Si-on-insulator　multilayer　platform　with　vertical　asymmetrical　directional　coupler　(ADC)　is　designed　and　analyzed.　The　vertical　ADC　is　consisted　of　two　waveguides,　which　are　placed　in　the　bottom　Si　layer　and　upper　SiN　layer　separately.　It　is　found　that　by　properly　choosing　the　values　of　the　structure　parameters,　especially　taking　advantages　of　the　extra　freedom　of　the　relative　location　between　these　two　waveguides,　the　performance　of　the　PBS　can　be　significantly　improved.　By　incorporating　tapered　structures　into　the　coupling　region　in　the　further　step,　bandwidth　of　294　nm,　which　is　determined　by　the　insertion　loss　of　＜1　dB　and　the　extinction　ratio　of　＞20　dB　in　both　polarizations,　is　realized　within　a　coupling　length　as　compact　as　6.9　mu　m.　The　proposed　device　has　a　good　potential　to　be　applied　in　three-dimensional　photonic　integration,　where　higher　integration　density　or　more　on-chip　functions　can　be　realized.