The processes of rapid solidification from liquid to solid and heating from glass to crystalline for Ni3Al are simulated using molecular dynamics method. An amorphous state can be obtained by rapid solidification as long as the cooling rate is sufficiently large, which is very difficult to get in experiment. An fcc-type crystalline is obtained by heating the amorphous with a small heating rate. Based on the pair analysis technique, the microstructures of liquid, supercooled liquid, amorphous, and crystalline states of Ni3Al have been analyzed. Furthermore, the effects of cooling rate and heating rate on microstructures of Ni3Al during rapid solidification and heating processes have been discussed.