Abstract: In order to solve the problem of lost circulation during infill drilling in mature blocks of the Qinshui basin, a 3D wellbore fracture model was developed based on the study of the actual well bore structure in the blocks, Ansys-fluent software is used to simulate the flow of conventional mud plugging, pressure mud plugging, gel mud plugging in formation fractures, and the simulation results are verified by field construction examples. The results show that the time of plugging (Gel plugging < Pressure plugging <Conventional plugging) , the return height of cementing annulus cement (Gel plugging > Pressure plugging > Conventional plugging); Combined with the advantages and disadvantages of the three lost circulation techniques, it is shown that the effect of gel plugging is better if a single point loss occurs and the lost circulation location is clear If the leakage point is more, and the leakage location is not clear, then the pressure plugging effect is better. In addition, compared with the conventional static plugging technology, the optimized plugging technology combined with wellhead pressure technology has the advantages of shorter plugging time, higher pressure bearing capacity of the lost formation and better plugging effect, and the required pressure bearing equipment is easy to make on the spot, simple operation, stronger applicability.