The H-mode pedestal and the Edge Localized Mode (ELM) driven by pedestal gradients are two crucial issues remaining in the focus of magnetic fusion research for last twenty years. The effect of transient peak loads on the divertor target plates due to ELM pulses is recognized as one of the most important aspects defining the design of future devices. In spite of big progress in the characterization of the H-mode pedestal, the ELM physics remains an open issue up to now. In the view of short time scale of ELM crash only a few diagnostics are able to follow the ELM dynamics. One of them is a reflectometry and some recent works have shown its ability. JET X-mode reflectometer operates at four fixed frequencies (76, 85, 92 and 103GHz) simultaneously. They are distant sensibly to give cutoff layers covering the pedestal region from top to foot in most H-mode plasmas. Our paper describes the recent results on the study of ELM dynamics with X-mode reflectometer in JET.