In　order　to　improve　the　water　environment　of　Songhua　River,　develop　and　maintain　a　healthy　water　cycle,　the　article　has　made　theoretical　and　mathematical　analyses　of　wastewater　treatment　and　reuse.　It　proposes　that　the　important　link　of　sustainable　utilization　of　urban　water　resources　is　wastewater　treatment　and　reuse,　and　the　main　approach　of　sustainable　utilization　of　water　resources　is　water　saving,　wastewater　reclamation　and　reuse.　Through　establishing　the　cost　equation　of　recycle　water　system　and　optimizing　it　by　Matlab,　an　optimal　treatment　scale　of　the　city　recycle　distributed　wastewater　system　is　obtained.　The　principles　of　recycle　water　system　in　northern　areas　are　put　forward　based　on　the　research　of　sustainable　utilization　of　water　resource　in　Songbei　district.　The　results　can　provide　experiences　and　references　for　water　saving,　wastewater　reclamation　and　reuse　in　northern　cities　of　China.