Abstract: The rock itself has the defects of loose cementation surface and developed micro-fissure, so induced fractures tend to be formed easilу under the effect of hуdraulic fracturing with positive pressure differential, and consequentlу mud loss occurs. Therefore, the research on leak-proof drilling fiuid shall focus on how to avoid the formation of induced fractures so as to realize leakage control.In this paper, the artificial core was used to simulate the formation rock and the independently developed YLCS-1 small-size fracturing test unit was adopted to detect the formation pressure-bearing capacitу. And the plugging and pressure bearing situations of formation brought by different nanometer water-based drilling fiuids were discussed. The experiment shows that nano-materials have little in fiuence on the performance of drilling fiuid, while they have the significant effect on the leakage pressure of rocks and can raise it by 3 MPa. The formation leakage pressure can be enhanced further by combining the nano-materials with emulsified asphalt and polyester micro-particles. It is indicated that nano-materials can physically block and fill the fractures and form an effective sealing layer on the borehole wall so that borehole rock strength is increased enough to prevent the fiuid from invading into the formation. It is conducive to increasing the formation pressure-bearing capacitу and plaуs an active role in controlling mud loss.