Due to the broken stratum, wall collapsing, landslide accidents and lost circulation happened frequently in the drilling of the second hole of Wenchuan earthquake fault scientific drilling project (WFSD-2). For preventing lost circulation during cementing, anti-leakage cementing technology with low density slurry was selected. Through multiple performance experiment of slurry, the formulation of low density slurry for anti-leak was optimized. This formulation was successfully adopted to cement the 168.3 casing in WFSD-2.