The range resolution of a streak tube imaging lidar (STIL) system is researched based on the parameter estimation theory. According to the theory of mathematics statistics, the Cramer-Rao low bound (CRLB) of range resolution estimate variance is analyzed. Streak tube lidar pulse model is researched, and the formulas of CRLB are given. The influences of range resolution of the STIL system are analyzed. The results show that higher signal-to-noise ratio values and faster streak tube sweep rate are both helpful in range separation estimation efforts. In addition, there is an optimal pulse-width that produces an optimal range resolution for a particular streak tube sweep rate.