This　paper　established　an　on-line　monitoring　model　for　fouling　resistance　of　cooling　water　based　on　heat　transfer　theory,　which　was　mainly　applied　to　the　fouling　resistance　test　for　condenser　of　chiller　in　operation,　and　the　test　requirements　were　presented.　It　proves　that　the　load　ratio　of　chiller　has　big　influence　on　the　test　result,　and　the　best　load　ratio　for　test　is　the　range　of　80%-100%.　A　case　has　been　executed　to　validate　the　model＇s　feasibility.