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Solitons can self-assemble into stable bound states, also denoted as soliton molecules that exhibit molecule-like dynamics. Soliton molecules have been predominantly investigated in the anomalous dispersion mode-locked fiber lasers. However, the soliton molecule dynamic evolution is still largely unexplored in the normal dispersion regime. We reveal here that, in the normal dispersion regime, the buildup and dissociation dynamics of soliton molecules. Our theoretical prediction indicates that, under different transmission functions of a saturable absorber (SA), a pair of solitons can be formed directly from background noise and then evolve into a soliton molecule through intense repulsive interaction, or a soliton molecule can be triggered to dissociate into a single soliton with transient annihilation and energy transfer. The experimental observation of short-time soliton molecule buildup and a new soliton molecule dissociation process corroborate the theoretical prediction. Furthermore, a long-time soliton molecule buildup ( ∼ 900 m s ) is discovered with single soliton splitting and soliton pair attraction. The buildup time is over four orders of magnitude longer than that of the short-time soliton molecule ( ∼ 21 µ s ). Our work unveils new perspectives into the ultrafast transient process and the interaction dynamics of soliton molecules in complex nonlinear systems.