Abstract: The transport process of neutral beam ions in HT-7Tokamak was simulated by Monte-Carlo method．The neutra-l plasma collision processes taken into account‚which include the charge-exchange‚ electron impact ionization‚ion impact ionization‚etc．The density distribution of neutral beam ions has been obtained．The simu-lated results show that neutral particles penetrate deeper with higher injection energy of neutral particles‚and the neutral atom density in Tokamak increases with the increase of injection flux of neutral particles．The density distribution of neutral atom is almost in agreement with the theoretical estimation at the plasma edge． 

Key words: neutral beam ions, density distribution, Monte-Carlo simulation