The effect of plasma screening has been investigated by incorporating the Debye potential into the framework of the relativistic Dirac-Fock method， and the GRASP92 code has been modified to perform the calculations. As an example, we have studied the plasma effecting on energy levels and transition probabilities of H-like ions embedded in dense and hot plasma. The following three important results have been obtained: （1） all energy levels are shifted away from their unscreened values toward the continuum, and the shift of energy increases as screening strength decreasing. Furthermore, for each eigenstate with given quantum numbers n and l, there is a finite value of λc （critical length） which corresponds a zero energy. （2） For a given transition, the oscillator strength and transition probability decrease with increase of the screening strength. （3）　The degenerate fine-structure levels with the same n, j but different l can be destroyed by the plasma screening effect, even without the consideration of the Lamb shift, which has received little attention in the past.