With the help of 25,000 Han Chinese and aborigines on Taiwan, Cheng cut all communications on the island and isolated the Dutch. He offered them surrender or annihilation.
國姓爺的軍隊在台島二萬五千漢人和本地原住民的歸附支持下，截斷一切海陸交通，也包圍普羅凡舍堡、隔絕熱蘭遮城，使兩地頓成孤城，隨即要求投降，否則屠戮全城。城內的荷蘭長官商議後，決定派員晉見國姓爺，提出與鄭家舊誼，希望取得協議。