Abstract: The equation of state of materials under extreme pressure and temperature conditions is important fundamental data in high energy density physics, planetary science, and inertial confinement fusion research. Traditional shock compression experiments are limited by the initial state of the sample and can usually only cover a limited thermodynamic region; in contrast, the static-dynamic compression technique combining static high pressure and laser-driven dynamic compression can significantly extend the accessible thermodynamic region by changing the initial density of the material. In this work, a high-precompression static-dynamic compression experimental technique for equation-of-state studies over a wide thermodynamic range is developed. By mechanically and optically optimizing the target structure of a mini-Boehler-type diamond anvil cell (DAC), the static precompression level is successfully increased to as high as 6.2 GPa. The experiments are carried out on the SG-II and SG-II upgrade laser facilities, and velocity interferometry (VISAR) and a streaked optical pyrometer (SOP) are employed for high-precision diagnostics of the shock process. Meanwhile, under high-precompression conditions, corrections are applied to the standard material equation of state, refractive index, and release path in the impedance-matching method. The experimental results show that this technique can significantly increase the initial density of the sample while maintaining good diagnostic signal quality, thereby extending the thermodynamic region accessible by shock compression experiments. Using hydrogen and deuterium as representative materials, the experimental data obtained from this platform show good agreement with theoretical models. The high-precompression static-dynamic compression experimental technique established in this work provides a new experimental approach for equation-of-state studies over a wide thermodynamic range.