A report from Carnegie Moscow Center said China bought the Su-35S so that it can compare it to its J-11 series.
By Aleksandr Medvedev (http://russianplanes.net/id78098) [GFDL or GFDL], via Wikimedia Commons
The Su-35 represents the most pinnacle of the Su-27/30 family and China wants to learn from Russia on how to maximize the potential of the platform.