var _tempTBL = (TextBlock) checkBox.Content; //Get handle to TextBlock
var text = _tempTBL.Text; //Read TextBlock's text

编辑：

在旁注中，您可以将所需文本直接设置为 CheckBox的内容。

On a side note, you can directly set desired text as CheckBox's content.

checkBox.Content = Hello World;

当您要访问文本时，不进行类型转换是必需的

And when you want to access the text, no type cast is needed

字符串text = checkBox.Content;