The　proliferation　of　distributed　energy　resources　and　the　introduction　of　new　loads　in　distribution　networks　present　significant　challenges　for　monitoring　and　operation.　To　satisfy　the　enhanced　observability　and　controllability　requirements　of　modern　distribution　networks,　there　is　an　increasing　demand　for　advanced　monitoring　devices.　Distribution　Network　Phasor　Measurement　Units　(DPMUs)　offer　high-precision　measurement　data　with　precise　timestamps,　thereby　improving　both　the　accuracy　and　redundancy　of　measurements　within　the　distribution　network.This　paper　introduces　an　optimization　model　for　the　strategic　placement　of　PMUs　within　distribution　networks,　leveraging　node　metric　indices.　The　indices　considered　are　node　degree,　spatiotemporal　correlation,　and　node　power　ratio.　The　relative　importance　of　these　indices　is　determined　using　an　improved　entropy　weight　method,　which　quantifies　the　differentiation　of　nodes　within　the　network.　This　method　facilitates　the　prioritized　placement　of　DPMUs　at　critical　nodes.　The　proposed　model　also　incorporates　constraints　such　as　the　depth　of　unobservability　and　zero　injection　nodes.　Utilizing　a　0-1　integer　programming　algorithm,　the　model　derives　a　multi-stage　optimal　placement　scheme　for　PMU　placement.　This　scheme　evolves　from　incomplete　observability　to　critical　observability　and　ultimately　to　full　redundancy.　Importantly,　this　approach　allows　for　the　monitoring　of　key　nodes　within　the　distribution　network　and　enhances　measurement　redundancy　without　necessitating　an　increase　in　the　number　of　placements.