In view of the problem that the formation of deepwater wells in the study area leak easily, the mechanism of loss-circulation was studied in depth, and the loss-circulation plugging material SmartGel was developed with guar gum and its derivatives as the main synthetic raw materials. The gel process could be controlled by adjusting the dosage and temperature of gel accelerators. In order to adjust the gelling speed of SmartGel, GelRetarder and GelAccelerant were developed. The extrusion strength of SmartGel increased with the increase in SmartGel dose and decreased with the increase in temperature. As for the plugging performance of SmartGel, the sand bed test confirmed that the pressure capacity of SmartGel in the 80 °C sand bed can reach at least 7 MPa, which can meet the requirements of site construction. The PPT sand tray test and core flow meter simulation pore test showed that SmartGel has good bearing performance. As for the gel-breaking of SmartGel, low-temperature gel-breaking was achieved by adding the biological gel-breaking agent S100. The gel-breaking time was shortened by increasing the dose of S100; the higher the temperature, the more obvious the effect. To facilitate high-temperature gel-breaking, the post-gel-breaking method was adopted since the enzyme gel-breaking agent cannot play a role above 60 °C. The test showed that after adding 5% gel-breaking agent PF-JPC, due to gel-breaking at 80 °C, the SmartGel gel completely reduced the viscosity within 48 h. We successfully used SmartGel + 0.2% GelRetarder to stop the loss-circulation in well A and used a cored well wall to show a good gel-breaking effect.