One of the most important ways for plasma heating is injection of the electromagnetic waves into the plasma. After injection of wave into the plasma, Parametric Instabilities by considering of match conditions for frequency and wave number can be occur. One of these instabilities that much considered is Stimulated Raman Scattering Instability that in this instability an electromagnetic wave decays into another electromagnetic wave and an electron plasma wave. Mechanism of this process is justifiable on the basis of the pondermotive force. . For heating of dense plasma in Magnetic Confinement Fusion, radio waves inject into the plasma too. For this way Stimulated Raman Scattering Instability occurs too. Instability rate in this way depends on pump frequency and density of plasma sensitively so that for pump wave frequency with frequencies 28, 58, 128 and 138GHz for NSTX, instability rate for 28GHz is high by order two compare to 128GHz. Resulting high value instability rate for 28GHz that leads to strong damping, shows that this frequency is efficient compare to three other frequencies for heating purpose in NSTX. Keywords : Parametric Instability, Stimulated Raman Scattering Instability, pondermotive force, Instability rate, Landau damping, NSTX tokamak.