X-ray spectra have been produced on "Shenguang II" multi-beam laser facility, in which the flat gold target was irradiated by array lens smoothing 0.53μm laser beam. The absolute conversion efficiency ξ_x is reported from the incident laser light energy to x-ray photons for laser-produced plasmas. The characterization of backlighting line sources having photon energies from 1.8 to 3.1 kev are studied under multi-beam laser driving target condition. Quantitative x-ray spectra and energies spectral distribution have been obtained as a function of laser power density and x-ray emission angle.