When high-speed nucleus comes into high temperature thermal equilibrium plasma，there exists a non-equilibrium relaxation process before the incident nucleus reaches a thermal equilibrium state with plasma if kinetic energy is far greater than the average kinetic energy of charged particles in background plasma. In the relaxation process，the kinetic energy of incident nucleus will be lost individually because of its interaction with background plasma. In this paper，we take high speed Tritium of 3MeV energy incident into high temperature LiD Plasma as an example，The reaction rate parameter of D(t,n)⁴He reaction in consideration of the non-equilibrium relaxation process of Tritium in the plasma is calculated. In the calculation，the energy losses of Tritium in plasma，caused by Coulomb Scattering Processes of electrons and variousions is considered，and the fast-ion unified slowing down theory in plasma proposed by C. K. Choi et al.is used to calculate the energy loss rate of Tritium. Both the D(t,n)⁴He reaction of beam-target mechanism in non-equilibrium state and the D(t,n)⁴He reaction in thermal equilibrium state are considered. Neglecting nuclear scattering and the interference between nuclear scattering and coulomb scattering，the calculated results show that，when the temperature of plasma varies in the range of 7.5KeV～20KeV，the correction factor to reaction rate parameter of D(t,n)⁴He in thermal equilibrium state caused by the non-equilibrium relaxation process of Tritium in Plasma is in the range of 1.0062～1.0943，and the higher the temperature of plasma is，the smaller the correction factor is. The results also show that，when the temperature of plasma is fixed，the correction factor slightly increases as the particle number density of plasma increases，but the change is not prominent.