The emission of light particles (LP),charged particles (CP),intermediate mass fragments (IMF) and the largest fragment(MAX) for 129Xe is investigated in the frame of lattice gas model.Definite turning points for the slopes of average multiplicity of LP,CP and IMF,mean mass of the largest fragment(Amax)and mean excitation energy per nucleon(E*/A)of the dissociation source against temperature are shown at 5—5.5MeV,where the largest variances of the distributions of LP,CP,IMF,MAX and E*/A are observed also.Furthermore,the slopes of these variances with temperature show discontinuities at the same temperature.All these features indicate that the largest critical fluctuation is simultaneously accompanied by the critical phenomenon and phase transition at the turning temperature in the lattice gas model.