To ensure the legitimacy of his future succession to his son. Sun Ce seems to have a son because he inherited it from his brother. If he makes Sun Ce emperor, what about Sun Ce's son? If Sun Ce has no son, after Sun Quan's death, if Sun Quan's son is younger, should everyone let Sun Quan's younger brother continue to be his younger brother? So let Sun Ce be king, though a bit excessive, but also for the sake of Sun Quan's stable rule in Jiangdong.