We present observations and analysis of an RS CVn-type double-lined eclipsing binary system, RU Cnc. The system has been observed for over a century. The high-quality long-cadence emph{Kepler} K2 C5 and C18, newly obtained observations, and two radial velocity curves were combined and analyzed simultaneously assuming multi-spot model. The masses, radii and luminosities of the component stars are precisely obtained as $M_textrm{c} = 1.386pm0.044, M_{_odot}$, $M_textrm{h} = 1.437 pm 0.046, M{_odot}$, $R_textrm{h} = 2.39pm 0.07, R{_odot}$, $R_textrm{c} = 5.02 pm 0.08, R{_odot}$, $L_textrm{h} = 11.4pm 1.2, L{_odot}$, $L_textrm{c} = 12.0 pm 1.0, L{_odot}$ and with a separation of $textrm{a} = 27.914 pm 0.016, R{_odot}$. The distance of the system is determined to be $380pm 57,$ pc which is consistent with the Gaia DR2 result. Long-term detailed period variation analysis of the system indicate a period decrease of $7.9times10^{-7}$ days per year. The results suggest the cooler component to be on the red giant branch (RGB) and the hotter one to be still on the main sequence.
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