Can any body tell me what is the equvalent tag in session bean for "<cmp-field>" in ejb-jar.xml
There really is no equivalent to this element for a session bean. Session beans to not represent persistent objects and do not use container-managed persistence, therefore would have no reason to use the element.
For complete information on what elements are used and where, take a look at the ejb-jar_2_0.dtd. It is commented rather thoroughly.