Based on the migration-coalescence mechanism for helium bubble growth in a material, the evolution of helium depth distribution during annealing is simulated by the Monte Carlo method. The factors that influence the evolution are studied. The results show that the initial concentration and radius of the helium bubble can affect the evolution of He depth distribution, while the annealing temperature has influence only on the evolution rate but little on the final depth distribution of helium. It is also shown that the evolution of the system turns to slow down gradually with the annealing time going.