Abstract: Recent progress in ultrafast laser technology has made it possible to generate pulses shorter than 2 cycles, so the accurate measurement of such pulses has become an important branch in ultrafast science. Based on the general description of the conventional autocorrelation method, we review the new developments in femtosecond laser diagnostics. In particular, two novel methods, frequency resolved optical gating(FROG) and spectral phase interferometry for direct electric field reconstruction(SPIDER), are described. Vario