Abstract: Spatial localized structure(solitonlike electromagnetic wave) has been observed following the interaction of an intense and short laser pulse with underdense plasma using the two dimensional PIC simulation.The formation mechanism and spatiotemporal evolution of the solitonlike wave and related phenomena such as the energy exchange process of electromagnetic field with plasma wave, the frequency downshift of laser pulse,and the caviton formation were discussed. Once EM wave oscilation frequence is lower than plasma frequcnce, the localized structure will appear and it is easier to form in higher initial plasma density.