  The PandaX-4T experiment, a four-ton scale dark matter direct detection
experiment, is being planned at the China Jinping Underground Laboratory. In
this paper we present a simulation study of the expected background in this
experiment. In a 2.8-ton fiducial mass and the signal region between 1 to 10
keV electron equivalent energy, the total electron recoil background is found
to be 4.9x10^{-5} /(kg day keV). The nuclear recoil background in the same
region is 2.8x10^{-7}/(kg day keV). With an exposure of 5.6 ton-years, the
sensitivity of PandaX-4T could reach a minimum spin-independent dark
matter-nucleon cross section of 6x10^{-48} cm^{2} at a dark matter mass of 40
GeV/c^{2}.
