Using the one-dimensional particle-in-cell simulation, we studied the splitting of ultrashort laser pulses propagating in plasmas and the generation of soliton-like structures, and compared the effect on these phenomenon by changing the duration and intensity of initial laser pulse. It was shown the solitons moving with high group velocities can be formed by the ultrashort laser pulse with in a few cycles of duration. When the pulse duration and intensity of initial laser pulses increase, the group velocities of solitons decrease with greater frequency down-shifts. The decay of high-order solitons are generated by self-steepening and self-frequency shift, so the initial laser pulse splits into several daughter_pulses, and two solitons with different group velocities can be formed and propagate in the plasma. The number of daughter-pulses observed in simulations has been predicted by the theoretical calculation of soliton-orders.