Lost circulation simulator is one of the key apparatus to formulate technical plans for lost circulation prevention and plugging. This new type medium pressure (0-1MPa) lost circulation simulator was designed to improve the complex structure, tedious test procedures, large volume mud and low data reappearance of existing lost circulation simulators. With this device, 1-3mm fracture leakage formation and 1-4mm cavern leakage formation can be simulated. The actual leakage area is totally 0.35-2.79cm2 with porosity of 1.81%-14.24%. By using this experimental device, the plugging slurry formulas, being composed of swelling plugging agents and walnut shells, etc., is obtained, which is suitable for different leakage formations. The sealing effect of plugging slurries not only depends on the size of fractures or cavern, but also on the total porosity of leakage formation. This lost circulation simulator and the plugging slurry formula can offer beneficial reference for lost circulation prevention and plugging in drilling process.