Using $.ajax to POST XML to MVC Controller method

var payload = '<?xml version="1.0" encoding="utf-8"?><data>XML_GOES_HERE</data>';
$.ajax({
    url: "/Data/SaveXML/",
    type: "POST",
    processData: false,
    contentType: "application/json; charset=utf-8",
    data: JSON.stringify({ payload: payload })
})

contentType设置为application/json，数据变成一个对象，然后通过该JSON.stringify方法运行，以确保querystring可以发送各种字符。