A robust starch-grafted nanocomposite preformed particle gel (SN-PPG) with superior viscoelasticity and thermal stability is developed to improve the oil recovery. The effects of a cross-linker, an initiator, starch, sodium montmorillonite (Na-MMT), and additives thereof were systematically studied. Through introducing starch and Na-MMT, the storage modulus of the swollen gel was ameliorated from 570 to 1420 Pa. At 80 degrees C, the SN-PPG exhibited thermal stability after aging for 90 days; meanwhile, it showed an inflection temperature of 187.3 degrees C in the differential scanning calorimetry measurements, which indicated excellent thermostability. Moreover, the SN-PPG displayed a reinforced pH and salinity tolerance compared with the conventional PPG. In core-flooding tests, the SN-PPG successfully blocked the fracture aperture and improved the oil recovery by 29.86-38.59%. Furthermore, the characterizations involving Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the decoration mechanism of starch grafting and Na-MMT nanocompositing. The results showed that the robust SN-PPG could be a candidate for remedying the conformance problem and improving the oil recovery for high-temperature and high-salinity reservoirs.