  One of the most prominent problems of optical/ultraviolet (UV) tidal
disruption events (TDEs) is the origin of their optical/UV emission. It has
been proposed that the soft X-rays produced by the stellar debris accretion
disk can be reprocessed into optical/UV photons by a surrounding optically
thick envelope or outflow. However, there is still no detailed models for this
mechanism. In this paper, by performing hydrodynamic simulations with radiative
transfer, we calculate the optical/UV emission of the circularized stellar
debris accretion flow/outflow system. We find that the optical/UV photons can
be generated by reprocessing the emission of the accretion flow in the
optically thick outflows. The model can well interpret the observed emission
properties of optical/UV TDEs, including the emission radius, the radiation
temperature and the luminosity, as well as the evolution of these quantities
with time, providing a strong theoretical basis for understanding the origin of
optical/UV TDEs.
