Abstract: A liquid proppant comprised of a phase-change liquid and a non-phase-change liquid was developed to effectively support the full fracture length and network in ultra-deep reservoirs. The developed proppant is liquid under the ground temperature, while it undergoes phase change under the high temperature in reservoirs and transforms into solid particles after a while to support fractures. In addition, it could maintain high fracture conductivity under high temperature and high closing pressures. The test results revealed that the liquid proppant could transform into solid particles of different sizes under different mixing speeds. Before the phase change, it was a viscous fluid, with low filtration loss and good compatibility. After the phase change, the subsurface self-generated proppant had a good pressure-bearing capacity, and the particle size and phase change time could be controlled. Under the closing pressure of 60 MPa, the combinations of proppants of different particle sizes could have an effective conductivity of 9.21 D·cm. The development of the temperature-responsive subsurface self-generated proppant can provide a new efficient stimulation method for oil and gas development in ultra-deep reservoirs.