Molecular dynamics simulation of nanoindentation on Al(111) surface is presented. The simulation is performed using the Ercolessi-Adams glue potential and the Berendsen thermostat. Boundary conditions of 'pseudo' thin film are imposed in order to focus on the dislocation motion in ultra-thin film. Nucleation and development of defects underneath the indenter tip are visualized, and the gliding patterns of dislocation loops are investigated with particular emphasis on the effect of film thickness. Simulation results show that the early emission of dislocation loop is highly dependent on the film thickness.