Abstract: Utilizing single photon incident method, the hard X ray continuum from interaction of intense ultrashort laser(130 fs,10 16 W/cm 2,744 nm) with solid plasma is measured. By use of Pb shielding and coincidence technology, the background counts are kept below 10 -4 per shot, which satisfies the low background requirement of single photon incident. The measured hard X ray spectrum coincides with theory prediction.