Improving the sealing ability of drilling fluids is the primary technical way to effectively solve the borehole instability in hard and brittle shale and coal. With the filtration loss for 30 minutes under specific temperature and pressure as the evaluation standard， the plugging characteristics of several plugging materials are experimentally studied. The results showed that the sealing effect of the materials increased with the addition amount except for ultra-fine calcium carbonate. The plugging effect of emulsified asphalt， emulsified paraffin， and oil-soluble phenolic resin deteriorated with increase of temperature， while the plugging effect of polythene glycol and polyester first deteriorated and then had a certain degree of recovery. Polyester and ultra-fine calcium carbonate can quickly plug micro-cracks. These plugging materials had a significant impact on the rheological properties of drilling fluids. Analysis of the plugging mechanism of each plugging material shows that different plugging materials have different plugging characteristics and are suitable for different temperature and pressure conditions. The plugging capacity of the water-based drilling fluid can be effectively improved only if the plugging material is selected depending on specific downhole conditions.