分析了超快电子枪处于扫描状态下电子束的传输特性，对飞秒量级的超短电子束脉冲通过偏转扫描系统时的偏转距离等物理量进行了数值计算。计算结果显示：为确保电子束能够顺利通过偏转扫描系统并最后轰击直径为30 mm的荧光屏，必须加一个700~1400 V的初始电压，以便抵消负斜坡扫描电压的作用；700~1400 V的初始电压和负斜坡扫描电压的共同作用，是扫描实验成功的一个前提。扫描实验成功的另一个前提是激发光电阴极的光路和控制扫描的电路之间的同步。讨论了前提一带给同步实验的巨大困难，并设计了一个可以在扫描实验中以较高效率调节光路延时的实验系统，该系统可解决脉宽测量实验中扫描斜坡电压信号和超快电子脉冲的同步难题。

The transmission characteristics of ultrashort electron beams of the ultrafast electron guns in scanning state were analysed, and the deflection distance of the ultrashort electron beams passing the deflectionscan system was calculated. The results indicate that the initial voltage must be within the range of 7001400 V to counterbalance the effect of the negative scan slope voltage, ensuring that the electron beams will pass the deflectionscan system and finally hit the phosphor screen of 30 mm in diameter, and the cooperative function of the initial voltage and the negative scan slope voltage is one of the two premises of the scan experiment. The other premise is the synchronization of the electrical and the optical signals. Following the discussion of the great difficulty caused by the first promise, an experimental system that can adjust the optical delay more effectively in the scan experiment was designed, which can facilitate the synchronization of the negative scan slope voltage and the ultrafast electron pulse.