Abstract: Based on a porous structure principle, the nano-foam Cu targets were developed with a thickness of 100 m, a porosity of 70%, the density ratio of 30% solids of Cu. Experiments had been carried out on XG-Ⅲ laser facility in Laser Fusion Research Center, China Academy of Engineering Physics. The minimum laser intensity was more than 1.61018 W/cm2 with a duration of 30 fs. A single-photon-counting X-ray CCD was used to measure K spectrum of the X-ray source. The X-ray yield was counted to achieve K peak photons of 2.9108 photossr-1s-1 from femtosecond irradiated nano-foam Cu. The K X-ray conversion efficiency (CE) reaches the maximum value 0.008 38%. Compared to the pressed Cu foil target, the average X-ray yields of nano-foam structures increased by 1.8 times. The results show that nano-foam structure can effectively enhance the energy absorbability of femtosecond laser and improve the conversion efficiency from ultra intense laser to hot electron and X-ray.