Criterion　of　differential　settlement　in　subgrade　is　useful　for　keeping　road　in　a　good　serving　condition.　The　theory　of　traditional　materials　strength　and　their　technologic　economy　are　applied　to　analyze　the　additional　bend　stress　of　the　pavement　structure,　the　equivalent　beam　of　elastic　foundation　and　influence　on　the　pavement　structure　of　an　uneven　settlement.　The　allowable　settling　ratio　of　pavement　index　(Δi)　is　got　and　is　used　to　appraise　the　uneven　settlement　standard　value　in　subgrade.　The　allowable　settling　ratio　of　pavement　index　is　applied　in　an　certain　widening　expressway　project　and　Δi0.36%　is　attained　by　the　analyzing,　calculating　and　adding　a　certain　safe　coefficient.　This　value　was　put　into　practice　and　is　effective　during　the　past　two　years.　Copyright　Protection.