Streak tube imaging lidar (STIL) is an active imaging system that has a high range accuracy with the use of a pulsed laser transmitter and streak tube receiver to produce 3D range images. This work investigates the effect of the time bin size on the range accuracy of STIL systems based on the peak detection algorithm. The numerical simulation indicates that the time bin size has a significant effect on the range accuracy, resulting in a modified analytical estimate of the range error. An indoor experiment with a planar target is carried out to validate the theory that shows the linear relationship between the range error and the time bin size. Finer 3D depth images of a fist model are acquired by using a smaller time bin size and the best range error of 0.003 m is achieved with the optimal time bin size of 0.07 ns.