A new technique of measuring light pulse with fundamental wave information is presented in order to surmount the difficulty of phase matching of tunable laser in second- harmonic wave method. The expressions of upper-envelope of interference correlation function of fundamental pulse are derived for Gaussian and hyperbolic secant pulse shapes. It is pointed out that the width of the envelope at ordinate of 1.72 (for Gaussian) and 1.76 (for sech) equals to FWHM of second-order intensity correlation curve for above shapes respectively. It is not necessary to double frequency for this method, the arrangement of experiment is simpler and the ratio of signal to noise is greatly raised. The measurement of single pulse is simply discussed.