In order to compensate the time dispersion between photocathode and anode in the streak tube, a time focus and time collimation system for electron bunch is presented. The time focus system is used to compensate the time dispersion in the process of accelerating. Then, the compensated electron pulse traverses the time collimation system. The energies of the electrons are equal as they emerge from the time collimation system. Therefore, the pulse width of the electron bunch is invariable in the latter transmission process. The system is simulated by using the Monte Carlo method and the finite difference method. The electron pulse with width of 500 fs is generated at the photo-cathode. The width of the electron pulse is shortened to 131 fs by using the time focus system. The time compression ratio is 3.8:1. Then, the pulse width maintains 131 fs by using the time collimation system. The time collimation ratio is 16.8%.