A recent proposed universal decay law (UDL) for alpha-decay and cluster radioactivity (CR) half-lives [C. Qi, F. R. Xu, R. J. Liotta, and R. Wyss, Phys. Rev. Lett 103, 072501 (2009)] that can accurately reproduce the experimental data was introduced starting from alpha-like R-matrix theory. The UDL formula depends only on the mass and charge numbers of the charged particle and the Q value. The new mass table AME2012 and the theoretical FRDM95, KTUY05, and WS2011 masses are used to determine the Q values. We systematically investigate the branching ratios of cluster radioactivity with respect to a decay for even-even superheavy nuclei (SHN) with Z = 104-120 using the UDL formula. It is found that cluster radioactivity can be compared to alpha decay in neutron-rich SHN.