Problems　such　as　the　expansion　of　impervious　areas　and　changes　in　underlying　surfaces　have　occurred　in　cities　due　to　rapid　urbanization,　along　with　an　increasing　probability　of　extreme　rainfall.　Based　on　the　normalized　building　index　(NDBI)　of　underlying　surfaces,　calculated　from　remote　sensing　images　in　the　Pearl　River　Delta　from　1990　to　2020,　this　study　determines　the　underlying　surface　changes　in　the　Pearl　River　Delta.　Based　on　the　hourly　rainfall　data　of　meteorological　stations　in　the　Pearl　River　Delta　region　from　1990　to　2020,　the　extreme　rainfall　indexes　are　calculated　to　analyze　the　changes　in　extreme　rainfall　in　the　Pearl　River　Delta.　Based　on　the　NDBI　of　underlying　surfaces　and　extreme　rainfall　calculated　in　the　Pearl　River　Delta,　the　evolution　of　underlying　surfaces　and　extreme　rainfall　is　analyzed,　as　is　the　correlation　between　them,　and　the　main　conclusions　are　as　follows:　(1)　From　1990　to　2020,　the　NDBI　in　highly　urbanized　areas　in　the　Pearl　River　Delta　was　higher　than　that　in　non-highly　urbanized　areas.　The　NDBI　in　highly　urbanized　areas　showed　an　increasing　trend,　and　the　growth　rate　tended　to　slow　down;　(2)　From　1990　to　2020,　extreme　rainfall　in　highly　urbanized　areas　of　the　Pearl　River　Delta　was　higher　than　in　non-highly　urbanized　areas.　Extreme　rainfall　in　both　highly　urbanized　areas　and　non-highly　urbanized　areas　showed　an　increasing　trend,　with　that　in　highly　urbanized　areas　increasing　faster;　(3)　The　positive　correlation　between　the　NDBI　and　extreme　rainfall　indicators　in　highly　urbanized　areas　is　more　significant　than　that　in　non-highly　urbanized　areas.