Abstract: In view of cementing mechanism of dual contacts in cementing and the practical problems in field operation, this paper makes a basic analysis of isolation system of dual contacts, describes its downhole behavior and determines iour crucial factors affecting upon dual contacts. The test was studied for the properties of dual contacts and the preliminary test results was introduced. A new understanding for the effect of filtrate cake upon dual contacts is presented as well as the cementing and sealing to barriers and the cementing quality of high and low pressure formation.