To reveal the mechanism of shock wave drag reduction by single nanosecond-pulse laser energy deposition, the interactions between single laser energy deposition and normal shock wave, the single laser energy deposition and bow shock wave in supersonic flow field were studied numerically. Dissociation and ionization of air usually were not taken into consideration in typical simulation method, so appropriate space distribution of laser energy deposition induced plasma cannot be obtained. Tear-drop initial energy distribution and finite rate reaction model were adopted in this work. The simulation results of shock wave and hot core evolution processes are in good accordance with those of experiments, which verifies the rationality of the proposed simulation method. The normal shock and bow shock wave under the condition of Maher number 1.92 are selected respectively. The incident laser energy is 10.1 mJ and 12 mJ. Results show that the hot core of laser energy deposition induced plasma cloud turns into low pressure symmetrical vortex ring after the interaction with normal shock wave. In the condition of bow shock wave, the shock wave drag induced by low pressure vortex ring is reduced, which formed after the shock wave. It is the main mechanism of shock wave drag reduction.