Space-time analogy relation was applied to discuss the generation and propogation of ultrashort laser pulses. By the analogy between the diffraction of gratings and the generation of pulses, the results of pulse shape and satellite lines have been derived directly and in terms of the analogy between the diffractive spread in free space and propogation effects of ultrashort pulses in medium with group velocity dispersion, pulse width broadening, chirp and their compensation with phase conjugated mirrors are discussed.