As Android operation system platform is widely used in smart phone, one important aspect should not be ignored -its security. As android is an open mobile platform, and also a programmable software framework, is it more safe than his competitor - Iphone, Symbian and so on？ This paper will present some security issues on the mobile phones, analyze the security principles and mechanisms based on the architecture and features of Android OS platform, then it will compare Android with some other mobile operation systems like Iphone, Symbian in area of security to make a conclusion that Android is a safe mobile OS to a certain extent.