Talbot effect of a grating under ultrashort pulses laser illumination is analyzed theoretically.In the experiment,ultrashort pulses laser is measured by a frequency-resolved optical gating (SHG-FROG) apparatus and the ultrashort pulses laser is expanded by a reflective expanded system.Experimental results are in good agreement with the theoretical analysis.Theoretically and experimentally investigations indicate that the contrast of Talbot images under ultrashort pulses laser illumination are remarkable decreased.In addition,the contrast of Talbot images are further decreased at longer Talbot distance and under shorter ultrashort pulses laser illumination.