Resolution:

Add a argument of AjaxPro.HttpSessionStateRequirement enum in your AjaxPro.AjaxMethodAttribute.

Here is a example:

[AjaxPro.AjaxMethod(AjaxPro.HttpSessionStateRequirement.Read)]

Now u can access ur Session value like this: this.Session["0"].ToString().

So easy,right?

Another question: How to use Cookie in AjaxMethod?

The answer is u can't access cookie by the ref of "this".

You should use HttpContext.Current Object.Like this: HttpContext.Current.Request.Cookies[Name].Value.

For more information about SessionStat in Ajax.Net,See AjaxGuide.doc.