When I update an item field from the current item, I also gets the html tag.How can I only get the value from the current item field.

What type of field is CAddress? Is it multiple lines of text with Rich Text enabled?

Well , the CAddress in single line of text and it is the  target  field . The Source field is Address , which is  Mutiline Line text and Rich Text enabled.

CAddress needs to be rich text to be able to parse the HTML or your source field needs to not be rich text. You could use Regular Expression to remove the HTML potentially, but that would be more headache.

Yes , your suggestion  worked for me, but  what if we have to copy different field types where the source and target field are of different types. 

From plain to rich will work just fine; from rich to plain is where you have the issue. Again, I would say that the best way to approach that would be using regular expression in your workflow to strip out that HTML, but I don't necessarily think that would be easy.

There is no specific or straight answer for this in my opinion and its all depends on the data types. I would suggest to check available inline functions (if any suites), string to integer workflow action depending on the situation.