Abstract: Based on study of femtosecond streak camera system and femtosecond electron diffraction system, the influence of photoelectron energy, angular distribution and space charge effect on photoelectron time and energy spread in photocathode-mesh acceleration region is analyzed using Monte Carlo simulation. When the ultraviolet and soft X-ray incident photocathode, the time spread values of six types of photoelectron initial energy distribution is given. The relationship of electronic time spread between emission current density and accelerating field is analyzed. Electrons redistribute themselves inside the pulse, a linear velocity chirp develops on the electron pulse in acceleration region, the energy dispersion changes differently from that in free propagation region. The analysis and findings are useful for the study of ultrafast electronic propagation dynamics and the design of femtosecond streak camera, femtosecond electron diffraction and energy compensation components.