A collinear arrangement of optical shutter with ultrahigh time-resolution is introduced. An ultrashort pulse of Nd:glass laser is used as an ignition pulse and CS2 liquid as Kerr medium. Correlation time of 15 picoseconds has been measured. We obtain that the full width of half maxium of 1.06μ ignition pulse and 5300A signal pulse are 12 picoseconds and 8 picoseconds respectively.