您可以这样做：

radio1.SelectedIndex = 1;

但是，这是最简单的形式和您的UI增长将最有可能成为问题。说，举例来说，如果一个团队成员的插入的在项目单选按钮列表上方选项2 但是不知道我们使用的幻数的在code-后面选择 - 现在的应用程序选择了错误的指数

But this is the most simple form and would most likely become problematic as your UI grows. Say, for instance, if a team member inserts an item in the RadioButtonList above option2 but doesn't know we use magic numbers in code-behind to select - now the app selects the wrong index!

也许你想看看使用FindControl为了确定列表项实际需要，通过名称，以及适当地选择。例如：

Maybe you want to look into using FindControl in order to determine the ListItem actually required, by name, and selecting appropriately. For instance:

//omitting possible null reference checks...
var wantedOption = radio1.FindControl("option2").Selected = true;