The cores with micro cracks were manufactured with metal foil and cementitious materials of different thickness, together with external cylinder of high temperature and high pressure water loss instrument and mud cup, the evaluation on micro crack plugging can be carried out. The verification is made by micro observation method and flow calculation method, the result shows that the micro cracks surface has a certain roughness and fracture opening is in accordance with the experimental design; the minimum crack opening is 3.33μm and the length of crack is 5～10cm. The manufacturing method of micro crack core is simple with high opening similarity. It is verified that the laboratory-made crack can be used to evaluate the plugging performance of drilling fluid plugging material, which provides core module for the evaluation experiment of micro crack sealing, and makes up the shortcomings of smooth crack surface by crack plate simulation and crack opening conversion when using porous media of sand bed, steel balls and sand plate.