I have tried this on Alloy Sample Site and using HTML.Raw worked for me 

e.g. 

Content Model

Content View

Edit Mode Content Property

Rendered Page

Hi Minesh Shah (Netcel)

  Thank you for your response.

  It is working for me also. But i wanted to use XhtmlString or TinyMCE controls.

  Do you have any reference for XhtmlString or TinyMCE controls ?

Regards

Binay Thakur

I'm a little confused you have a string property currently on the content type, do you want to change this to an XhtmlString ? Or do you want to  cast the content to an XhtmlString and than use PropertyFor ? 

If you want to change 

public virtual string TestProperty {get; set;}

to 

public virtual XhtmlString TestProperty {get; set;}

My advice would be to create a new XhtmlProperty with a custom getter which gets the Data from the original property if Null and also hide the original property from the editors e.g. 

    [UIHint(UIHint.Textarea)]
    [ScaffoldColumn(false)]
    public virtual string TestString { get; set; }

    public virtual XhtmlString TestXhtmlString
    {
        get
        {
            var x = this.GetPropertyValue(p => p.TestXhtmlString);
            if (x == null)
            {
                return new XhtmlString(TestString);
            }

            return x; 
        }

        set
        {
            this.SetPropertyValue(p => p.TestXhtmlString, value);
        }
    }