Twelve 1,3-dihydroxylxanthones (3a～3l) were synthesized under the catalysis of Eaton's reagent applying phloroglucinol and substituted salicylic acids as starting materials. The yields were from 63% to 87%. The reaction mechanism and their structure-reaction activity relationship have been discussed. The clearance effections of all the prepared xanthones against nitrite have been investigated by UV spectrophotometry. It is disclosed that all the tested xanthones have obvious clearance effections against nitrite at the conditions of pH 3, room temperature, and 30 min treatment. 3b and 3f are identified as the most active compounds with clearance rate up to 34.0%. The clearance mechanism of xanthones against nitrite and their structure-activity relationships were also included here.