  Clusters of galaxies are merging during the formation of large-scale
structures in the Universe. Based on optical survey data, we identify a large
sample of pre-mergers of galaxy clusters and merging subclusters in rich
clusters. We find 39,382 partners within a velocity difference of 1500 km/s and
a projected separation of 5r_{500} around 33,126 main clusters, where r_{500}
is the radius of the main cluster. Based on the galaxy distribution inside rich
clusters with more than 30 member galaxy candidates, we identify subclusters by
modeling the smoothed optical distribution with a two-component profile, and a
coupling factor is obtained for merging subclusters in 7845 clusters. In
addition, we find 3446 post-collision mergers according to the deviations of
brightest cluster galaxies from other member galaxies, most of which have been
partially validated by using the Chandra and XMM-Newton X-ray images. Two new
bullet-like clusters have been identified by using the optical and X-ray
images. The large samples of merging clusters of galaxies presented here are
important databases for studying the hierarchical structure formation, cluster
evolution, and the physics of intergalactic medium.
