  The PandaX-III experiment uses a high pressure xenon gas TPC to search for
the NLDBD of $^{136}$Xe. The Microbulk Micromegas will be used for charge
amplification and readout in order to record both the energy and track of an
event with high energy resolution and spatial resolution. In the first phase of
the experiment, we are building a detector which contains 140 kg 90\%
$^{136}$Xe enriched gas operated at 10 bar. The detector will be installed in a
dry shielding system at CJPL-II. In this paper, we wil report the design of the
PandaX-III detector, including the shielding of the experiment and the
components of the TPC: the high pressure vessel, the readout plane and the
electric field cage.
