Carbon nanotubes (CNTs) and graphene (Gr), which represent one- and two-dimensional carbon nanomaterials, respectively, are two commonly used reinforcing materials in metal matrix composites (MMCs). In this study, molecular dynamics simulations of the nanoindentation behavior of CNT- and Gr-reinforced aluminium (Al) matrix composites (i.e., CNT/Al and Gr/Al) with the same structures were performed to study the compressive strengthening effect and indentation deformation behavior of CNTs and Gr on aluminium matrix composites. The simulation results show that the plastic deformation of Gr/Al during nanoindentation is significantly smaller than that of CNT/Al, whereas CNT/Al exhibits CNT dents when the indentation depth is larger. The hindering effect of Gr on dislocations is significantly better than that of CNTs, and the proportion of immovable dislocations in Gr/Al increases with increasing indentation depth, which can further improve the dislocation strengthening effect. As a result, the combined compressive properties and the ability to hinder large deformation of the matrix of Gr/Al are superior to those of CNT/Al.