The temporal performance of framing tube can be effectively promoted by pulse-dilation technology. However, the pulse jitter causes the exposure time jitter, which reduces the reliability of the tube. In order to discuss the reason and the improvement method of the exposure time jitter, the measurement, errors analysis and modification of exposure time are carried out. The results of the analysis of 200 dynamic images show that the jitter scope of the exposure time, caused by pulse jitter and inconsistency of dilation slope, is in the range of 11-26 ps. And the evaluation value of the exposure time of the tube is about 17.3 ps by using weighted means method according to the characteristics of dilation pulse and the distribution ratio of exposure time. Using the initial amplitude of the stretching pulse to correct the synchronization voltage, the deviation between the measurement value of the exposure time measurement and the theoretical value is reduced from ~9.8% to ~1.7%, which effectively increases the credibility of the measurement value. The study results provide the theoretical reference and technical support for the improvement of the reliability of the exposure time of the tube.