The present invention discloses an investment allocation system for managing investment return and risk and method thereof. The investment allocation system comprises a storage unit, a return rate computation unit, a standard deviation computation unit, an operation unit, and an allocation process unit. The storage unit stores a threshold, first data sets, and second data sets. The return rate computation unit transforms the data sets into return rate sequences. The standard deviation computation unit transforms the return rate sequences into standard deviation sequences. The threshold is assigned to the first standard deviation sequence in order to obtain a corresponding kth-quantile thereof. Further, an operation unit locates an object according in the kth-quantile into the second standard deviation sequence. The operation unit further processes the second standard deviation sequence to obtain a robustness index. Also, an allocation process unit allocates assets by processing the robustness indexes.