In this paper the time characteristics of soft X-ray diode (XRD) is studied. XRD is the importance component of soft X-ray spectrometer,which measures the soft X-ray spectrum emited by laser-plasma.The experiment utilizes the 200TW laser facility with energy ～6J　and pulse width ～30fs at the Laser Fusion Research Center of CAEP.The Au foil target irradiated by laser pulse produced X-ray emission, the filter(Al)-XRD system measures the X-ray signal.The high frequency cable (SUJ-50) transmits the electrical signal, a broad band oscillograph (TDS694C and TDS6604B) registers the signal.Linearity fit and comparison analysis of experimental data are performed.