Concerning　the　overlap　of　ground　penetrating　radar　(GPR)　signal　reflections　at　the　different　asphalt　layers,　which　reduces　the　measurement　accuracy　of　asphalt　surface　thickness,　the　WRELAX　algorithm　for　time-delay　estimation　was　adopted　to　analyze　the　air-launched　GPR　signal　reflections　with　1GHz　center　frequency　for　the　purpose　of　improving　the　detection　accuracy　of　thin-layer　thickness　of　asphalt　pavement,　and　simulation　and　field　test　were　carried　out　to　verify　the　effectiveness　of　the　proposed　method.　The　results　show　that　(1)　WRELAX　time-delay　estimation　algorithm　detects　iteratively　strong　reflections　and　then　subtract　them　from　the　original　signal　to　reveal　the　weak　reflections,　thus　protruding　the　time-delay　and　the　amplitude;　(2)　WRELAX　algorithm　in　1GHz　GPR　signal　processing　can　effectively　detect　thin-layer　thickness　of　asphalt　pavement,　with　relatively　small　variation　ranges　of　estimation　error;　(3)　WRELAX　algorithm　in　1GHz　GPR　signal　processing　is　robust　and　is　more　effective　than　that　in　2GHz　GPR　signal　processing;　and　(4)　the　maximum　relative　estimation　error　of　thin-layer　thickness　estimated　by　WRELAX　algorithm　is　less　than　5%,　which　meets　the　requirements　for　detection　and　evaluation　of　thin-layer　thickness　of　asphalt　pavement.　©　2018,　Editorial　Department,　Journal　of　South　China　University　of　Technology.　All　right　reserved.