Understanding　the　relationship　of　the　latency　among　network　nodes　is　important　to　cope　with　the　problems　of　network　measurements.　There　are　some　researches　touched　on　this　point　but　seldom　explicit　studies.　In　this　paper,　we　study　the　similarity　of　the　network　nodes　based　on　RTT.　And　have　some　new　conclusion　mainly:　Similarity　between　two　nodes　will　change　little　when　just　make　the　short　of　the　two　private　path　lengths　much　shorter.　Also,　similarity　will　very　close　to　each　other　when　their　path　ratios,　which　are　the　ratios　of　the　common　path　lengths　to　the　long　private　path　lengths,　keep　the　same.　Then,　we　found　that　similarity　is　the　same　mutational　trends　with　path　ratio　within　a　certain　load　combination.　At　last,　we　point　out　which　path　ratios　mean　the　strong　similarity　between　the　two　nodes　and　which　correspond　to　the　weak　correlation.　©　2010　IEEE.