Abstract: The method for measuring the spectrum of ultrafast high energy pulsed laser in picosecond pulse width was presented with combination of photoelectrical spectrography and streak camera. The operating principle of streak camera and spectrophometric principle of plane diffraction grating were described respectively. Through thorough analysis, we pointed out that the spectral measurement of ultrafast high energy pulsed laser with wavelength in 300nm~1600nm and pulse width above 2 ps could be achieved by using our described facility. The streak image was obtained by utilizing ultrafast high energy pulsed laser in 1054nm wavelength, and the measured spectral curve was derived by processing the data of streak camera, then the actual spectral curve was also given by calibrating the related energy parameters, the method for measuring the spectrum of ultrafast high energy pulsed laser in picosecond pulse width was proved. The influence of coupling lens on measuring spectrum and grating fiber-s dispersion angle on streak image were analyzed finally, furthermore the role of spectrum for ultrafast high energy pulsed laser with picosecond pulse width was discussed. With the rapid development of the technology for manufacturing streak camera, the method will be used for measuring the spectral curve of laser with femtosecond pulse width.