The dispersion of carbon nanotubes (CNTs) in water under thermal excitation has been investigated by molecular dynamics (MD) simulations. The pressure and temperature distribution of the combination of CNTs and water indicate that water molecules have increased kinetic energy under thermal excitation. The absolute value of the potential of mean force (PMF) and the mean square displacement (MSD) of CNTs significantly increase with the increase of temperature in the thermal excitation region. It can be concluded that CNTs have a higher tendency of separation at higher temperatures with the assistant of water.