Abstract: As drilling wells continue to move into deep ultra-deep layers, the requirements for temperature resistance of drilling fluid treatments are getting higher and higher. Among them, blocking agent, as one of the key treatment agents, has also become a hot spot of research. In this study, a high temperature resistant strong adsorption rigid blocking agent (QW-1) was prepared using KH570 modified silica, acrylamide (AM) and allyltrimethylammonium chloride (TMAAC). QW-1 has good thermal stability, average particle size of 1.46 μm, water contact angle of 10.5°, has a strong hydrophilicity, can be well dispersed in water. The experimental results showed that when 2 wt% QW-1 was added to recipe A (4 wt% bentonite slurry+0.5 wt% DSP-1 (filtration loss depressant)), the API filtration loss decreased from 7.8 to 6.4 mL. After aging at 240 °C, the API loss of filtration was reduced from 21 to 14 mL, which has certain performance of high temperature loss of filtration. At the same time, it is effective in sealing 80–100 mesh and 100–120 mesh sand beds as well as 3 and 5 μm ceramic sand discs. Under the same conditions, the blocking performance was superior to silica (5 μm) and calcium carbonate (2.6 μm). In addition, the mechanism of action of QW-1 was further investigated. The results show that QW-1 with amide and quaternary ammonium groups on the molecular chain can be adsorbed onto the surface of clay particles through hydrogen bonding and electrostatic interaction to form a dense blocking layer, thus preventing further intrusion of drilling fluid into the formation.