Abstract: The picosecond gated characteristics of X-ray framing camera at different DC bias are examined using sub-ps X-ray source produced by SILEX-Ⅰ facility. The point-source measurement of XFC exposure-time is set up. The dynamic gain is defined based on the XFC principium. The experiment shows that the widening of exposure-time is 10 ps at DC bias of -100 V, and the dynamic gain increases by a factor of 3.5. The amplitude of exposure-amount measured is on the high side at DC negative bias. It is possible that the DC bias influences the dynamics of original photoelectrons, and induces dynamic gain exaltation.