The main factors to threaten large and middle mammals on Zhoushan Islands are area loss, fragmentation,quality descending of the natural habitats which are resulted from human activities and hunting.The arealoss of the natural habitats has lost 56.3%. The natural habitats have been fragmented into manyfragments, and the fragmented degree has being deeped, and the quality of the natural habitats was declinedin 1912~1950. The threatened history of the large and middle can be divided into three periods.Before 1912 the large and middle mammals were threatened lighter; the middle and large mammals were threatened heavily in 1912~ 1950, and the main threatening factors were area loss, fragmentation andquality descending of the natural habitats. The large and middle mammals also have been threatened heavilyin 1950 - present, and the main threatening factors are the area loss and fragmentation of the natural habitats and hunting. The area loss, fragmentation and quality descending of the natural habitats haveimportant influences on the large and middle mammals extinction. The area loss and fragmentation of thenatural habitats and hunting are mainly responsible for endanging, distribution reducing and populationdeclining of the large and middle mammals. The social, political, economical factors and so on determine the rate of matural habitat area loss, fragmentation and quality changes and hunting level.