Abstract: According to the basic principle of "force-chain" in micro-granular matter mechanics, the key fine technical indices were proposed to evaluate the particle strength, particle elasticity and surface friction of loss protection and sealing materials, so as to solve the technical difficulties in loss protection and sealing of drilling fluid. Meanwhile, the corresponding experimental characterization method was established to reveal the pressure containment and tight plugging mechanism of drilling fluid at the micro-nano scale and put forward the optimization method of tight plugging drilling fluid, i.e., using reasonable particle types, particle size gradation and concentration control, rigid particles, elastic particles and fibers were synergized to plug fractures, so as to form tight pressure containment and sealing zones with a strong force chain network and greatly improve the formation pressure containment ability. The newly-developed experimental apparatus for evaluation and dynamic simulation on the plugging characteristics of drilling fluid can simulate the loss and plugging process of fractures with different widths under different formation temperatures and pressures, providing a experimental method for pressure containment and tight plugging mechanism and plugging effect evaluation. Using this novel plugging dynamic simulation equipment, the strengthened tight-plugging formulas are also optimized for drilling fluid at the wedge fractures with different widths, which exhibits the tight plugging characteristics self-adapting to fracture widths with pressure resistance up to 8 MPa, thus improving the pressure containment ability of formations significantly.