The study of radiation time property for cavity target heated by laser is reported. Laser wavelength of 1.053 μm, energy 30～750 J, pulse wideth 600～1100 ps with Gaussian shape are used to the target. The radiation time property of the source region are measured by two sub-keV X-ray energy specttometers respectively through laser incidence hole and X-ray transmission hole. The emission X-ray time history of source region and the relation of pulse width with emission hole area, hole shape,emission energy region and laser irradiation intensity et al. are given.