First, Jiangge has something in the hands of the dean.
Before the plastic surgery, Jiangge was brilliant, but his life was not satisfactory. After the plastic surgery, her career began to flourish. You know, as a plastic surgeon, the dean knows very well what Jiangge used to look like, which is also the biggest hidden danger of Jiangge. After all, as long as the dean exposes Jiangge's plastic surgery, his life and career will be greatly affected. This is absolutely unacceptable to Jiangge, and she doesn't want to see it. In other words, the dean holds the handle of Jiangge. Jiangge doesn't want this handle to ruin his life and let himself go back to the past, so Jiangge will kill the dean.
Second, Jiangge is fed up with the life manipulated by the dean.
According to the plot, although Jiangge made some achievements in his career after plastic surgery, he was threatened by the dean because of plastic surgery. Even after discovering that Jiangge had the idea of going to other places, the dean called her to warn her, which led Jiangge to give up the plan. After all, she can't accept the consequences of falling from the clouds to the ground. In other words, Jiangge has always been subject to the dean because the handle is in the hands of the dean. And according to Jiang Ge's self-report in the play, we can know that she has actually had enough of this manipulated life. Under such circumstances, Jiangge will naturally think of killing the Dean, so Jiangge knows that the Dean is a very important hidden danger for her. Jiangge understands that as long as this hidden danger is not eliminated, she will never have her own life.
Generally speaking, the reason why Jiangge killed the dean of plastic surgery hospital was that there was something in Jiangge's singer, and on the other hand, Jiangge was fed up with the life controlled by the dean.