Regulatory　signs　are　the　most　important　facility　for　conveying　traffic　laws　or　regulations　to　road　users.　At　nighttime,　the　effect　of　regulatory　signs　is　utterly　dependent　on　retro-reflective　sheeting.　In　the　natural　environment　and　real　traffic　conditions,　retro-reflective　sheeting　is　affected　by　diversified　components　and　retro-reflectivity　will　continuously　deteriorate.　When　retro-reflectivity　decreases　to　a　certain　level,　the　visibility　of　traffic　signs　will　fail　to　achieve　the　needs　of　road　users.　To　obtain　the　deterioration　characteristics　of　Regulatory　signs,　researchers　took　continuous　observation　of　120　guide　signs　put　in　the　test　square　over　twelve　years　(1998-2010).　According　to　the　data,　the　researchers　got　the　deterioration　curve　of　the　Coefficient　of　Retro-reflection,　furthermore,　the　researchers　built　a　mathematical　model　containing　a　linear　mathematic　model,　a　second-order　polynomial　model　and　a　cubic　curve　regression　model.　This　research　shows　that　normally　the　second-order　polynomial　model　and　cubic　curve　regression　model　have　better　fitting　than　the　contained　linear　mathematic　model.　The　mathematical　model　can　be　considered　the　basis　of　researching　the　guide　signs　sheeting　deterioration　characteristic　and　Life　cycle.　This　research　will　give　reference　to　Chinese　traffic　sign　maintenance.　©　2012　American　Society　of　Civil　Engineering.