China Academy of Engineering Physics Terahertz Free Electron Laser(CTFEL) needs a terahertz switch for picking of single-pulse, which can facilitate the experiments that require high peak power but low average power. With the self-induced plasma switching technology, single pulses can be reflected by a plasma mirror on a slab that is generated by short pulse laser. The critical density of the plasma and the threshold of the laser power density are calculated and the numerical simulation of the laser targeting process is carried out by using the radiation fluid simulation software. The simulation results show that the plasma density generated by the laser is much larger than the critical density, which proves the feasibility of the experiment. In addition, the parameters of the experimental equipment and the experimental optical path design are given.