i might misunderstood u.....

"当我打开新的form的时候，之前的那个form显然没有真正关掉"
--new created instance of form takes control and old form never get closed until u close the front one(new one).

in other word: this.close() never get executed unless u close ur new form.

As far as i know, it's normal and ur code runs as intended.

relex, ur code's just fine~~