People cannot witness the stellar evolution process of a single star obviously in most cases because of its extremely secular time-scale, except for some special time nodes in it (such as the supernova explosion). But in some specific evolutionary phases, we have the chances to witness such process gradually on human times-scales. When a star evolved leaving from the main sequence, the hydrogen nuclei fusion in its core is gradually transferring into the shell. In the Hertzsprung-Russell diagram, its evolutionary phase falls into the Hertzsprung gap, which is one of the most rapidly evolving phases in the life of a star. Here we report a discovery of a rapidly evolving high-amplitude $delta$ Scuti star KIC6382916 (J19480292+4146558) which is crossing the Hertzsprung gap. According to the analysis of the archival data, we find three independent pulsation modes of it, whose amplitudes and frequencies are variating distinctly in 4 years. The period variation rates of the three pulsation modes are one or two orders larger than the best seismic model constructed by the standard evolution theory, which indicates the current theory cannot precisely describe the evolution process in this rapidly evolving phase and needs further upgrades. Moreover, the newly introduced Interaction Diagram can help us to find the interactions between the three independent pulsation modes and their harmonics/combinations, which opens a new window to the future asteroseismology.
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