We investigate a control systems analysis on HIV infection dynamics with regard to enhancement of the immune response. The HIV dynamic model is modified to include the pharmaco-kinetics and pharmacodynamics of antiretroviral HIV drugs, and the intake of drug is considered as impulsive control input. As it is administrated at discrete time instants, we assume that this yields an impulsive control problem for a nonlinear continuous-time system. Based on this new model, we study clinical experiments about antiretoviral treatments via numerical simulation and analyse the experimental results. It is noted that this modeling approach can help to provide a theoretical explanation of the clinical results. The analysis result in the paper could imply that the protocol of the experiment might enhance the immune response against HIV.