In order to understand the phenomenon of plasma hot core evolution in air deposited by nanosecond-pulsed laser energy, a high-resolution schlieren system was set up by using two cameras with different resolution. The experimental results obtained from schlieren system showed a good illustration of the initial moment of laser energy deposition, and then the law of the two key parameters of pulse energy and lens focal length on the evolution of laser-induced plasma hot core were studied. The experimental results show that the higher the energy of laser deposition, the larger the size of the plasma hot core, but there may be saturation of the laser energy deposition. In addition, the higher the laser energy and the shorter the focal length of lens, the later the external air penetrates the plasma core after laser energy deposition, which means the plasma core can maintain a steady state of high temperature and low density for a long time, and provides sufficient reaction time for the relevant research on plasma active flow control from the laser energy.