We have derived a set of motion equations for the amplitude,the inverse pulse width,the chirp,the frequency,the central position of the pulse and the phase in a mode locked solid-state laser.In the hypothesis of the low and white noise,the timing jitter induced by the amplified spontaneous emission was estimated for a Ti:sapphire laser with the chirp.It is found that for a certain mode-locked solid-state laser with a pulse profile of sech2(1.763t/τ),the jitter is approximatively a linear function of the net group delay dispersion (GDD),and turns to be larger with increasing GDD ;however,it cannot be reduced to zero even if the GDD is completely compensated.