Abstract: In order to solve the leakage problem in cementing operation,a new plugging spacer fluid has been developed.The particle size and range of plugging material were determined according to the theory of grain composition,and Vermiculite particles and Polypropylene fiber selected as plugging materials.Taking MS spacer as a base fluid,made by MS chemicals and high temperature additive,the rheological property,stability,distribution of fiber,compatibility and flushing ability were evaluated.Plugging ability of the spacer was also evaluated with crack-plate plugging and sand bed plugging experiment.The results show that the performance of the MS plugging spacer fluid meets all the requirements for cementing,and its plugging pressure-bearing ability reaches 8 MPa.The MS plugging spacer fluid was applied successfully during φ219.1 mm liner cementation in Well Heba107.Field applications of 53 wells in northeastern Sichuan area and Tahe Oilfield have got good plugging results.