Abstract: For the measurement of the time profile and the contrast information of the ultrashort laser pulse, based on the third-order intensity correlation principle, using optical pulse replication, a measurement method is proposed. Theoretical analysis is made about the measurement method. The simulation was done with split-step Fourier and Runge-Kutta methods. By measuring the pulse with pieces of windows and piecing the windows together, the measuring range can be enlarged. Thus a high resolution and large window measurement is achieved. The pre-pulse and main pulse are separated into different windows to avoid the use of gradient attenuator, and provides high-contrast measurement capability.