Abstract: Physical considerations of hohlraum target design and methods of experimental investigations of laser energy absorption, X-ray conversion and plasma closure effects are presented. A series of physical phenomena observed in the experiments are given. By analyzing the phenomena. We conclude that the efficiencies of laser energy absorption and X-ray conversion of hohlraums are much higher than those of planar targets and also the efficiencies can be improved at lower power densities by using a focusing lens of larger relative aperture.