In　order　to　investigate　the　mechanism　of　how　to　control　scale　formation,　a　formula　of　resistance　force　to　control　scale　formation　process　was　proposed　through　analyzing　the　calcium　sulphate　scale　over　heated　face.　The　higher　velocity　of　slow　and　the　lower　super　saturation,　the　more　easily　the　surface　reaction　tends　to　dominate　the　whole　process.　The　lower　velocity　and　the　higher　super　saturation,　the　more　easily　mass　transfer　tends　to　dominate　the　process,　especially　under　the　condition　of　higher　temperature　difference　in　liquid-wall　and　with　high　wall　temperature.　During　the　period　of　scale　growth　controlled　by　convection　of　mass　transfer　and　surface　reaction　together,　surface　reaction　would　become　to　control　the　process　only　when　the　wall　temperature　were　steady,　but　the　control　mechanism　would　last　without　change　when　the　heat　flux　was　constant.