K-shell absorption spectroscopy of radiatively heated Al sample is reported. The experiment was conducted on Shenguang-Ⅱ Laser facility. Eight main beams of the facitliy are injected into a conical gold cavity to produce high-temperature X-ray heating source. This X-ray source is then used to irradiate an Al foil located in the center of the cavity, and heat the foil to temperature of tens of electronvolt. After a time delay, a ninth short-pulsed laser beam is focused on a gold disk to generated an X-ray point-backlighter. By measuring the spectra both directly from backlighter and attenuated by the heated sample in the wavelength range of 075—085nm, the K-shell absorption spectrum of Al is obtained. By fitting the experimental spectrum with theoretical calculation, electron temperature of the heated sample is determined.