The　method　of　differential　imaging　to　detect　high　intensity　focused　ultrasound　(HIFU)-induced　lesion　combined　with　lesion　evaluation　method　by　measuring　the　variation　of　attenuation　of　soft　tissue　with　log　spectral　difference　algorithm　was　proposed.　Experimental　results　of　bovine　muscle　and　liver　in　vitro　were　acquired.　The　performances　of　several　lesion　detection　algorithms　including　absolute　difference　(AD),　sum　absolute　differences　(SAD)　and　sum　squared　differences　(SSD)　were　analyzed　with　several　window　sizes　and　threshold　values.　Then　three　attenuation　parameters　to　evaluate　degree　of　tissue　damage　were　compared.　It　is　shown　that　variation　of　the　mean　attenuation　calculated　in　the　range　of　bandwidth　of　transducer　Δᾱ　is　an　effective　parameter　to　evaluate　lesions.