Peak output powers of solid-state laser facilities have tremendously increased by a few orders of magnitude since the middle of last eighties due to the combination of the technique of chirped pulse amplification (CPA), advanced high-power laser technologies and novel laser materials. Petawatt (PW) level laser facilities have been built for picosecond and femtosecond pulses with focused intensities of up to 1020～1022 W/cm2. Laser intensities play dominant roles in understanding the physics of laser-plasma interactions and, therefore, different intensities open different physics areas to study. Such high laser intensities are able to produce extreme conditions: ultraintense electric and magnetic fields, and ultrahigh pressure, leading to the emerging of strong-field physics. A numbrer of multidisciplinary frontiers have been explored, such as particle acceleration, intense radiation source, advanced light source, attosecond physics, fast ignition fusion, superhot matter, nuclear physics, ultrafast proccess diagnosing, laser astrophysics, nonlinear quantum electrodynamics (QED) and so on. Also, there exist invaluable potentials in material, biological and medical applications.