The collision dynamics of the fast ion population in ultra-dense DT plasmas are investigated and analyzed within the framework of the relativistic Fokker-Planck equation. The Green function expansing on the spherical harmonics is used to express the solution of the equation. With the Green function we can calculate the stopping time, the ion range, the straggling range, and the mean transverse dispersion of different kinds of ions in plasmas. Compared to the previous ways of studying the movement of ions in plasmas, we not only calculate the straggling range without the approximation that the energy loss of the ions is much smaller than the energy of the ions, but we also calculate the stopping time and the mean transverse dispersion. This calculation is important for the experimental study of high energy density plasmas and fast ignition of laser fusion.