step1: 下载Android SDK Manager
step2: 安装之后若出现 Failed to fetch URL https://dl.google.com/android/repository/addons_list-2.xml, reason: Connection to https://dl.google.com refused ...
之后选择在Android SDK Manager主界面左上角选择-->「Tools」-->「Options…」，弹出『Android SDK Manager - Settings』窗口。
step3:在窗口上「HTTP Proxy Server」和「HTTP Proxy Port」输入框内填入mirrors.neusoft.edu.cn和80
选中「Force https://… sources to be fetched using http://…」复选框即可。