自己搞定了!
 SOAPHeaderElement    soapHeaderElement = new  SOAPHeaderElement(new javax.xml.namespace.QName("http://www.com","SMSSoapHeader"),"SMSSoapHeader");   
        
        soapHeaderElement.setNamespaceURI("http://www.com/");   
        
        
        try
{   
soapHeaderElement.setObjectValue(null);
soapHeaderElement.addChildElement("Username").setValue("aaaaa");
    soapHeaderElement.addChildElement("Password").setValue("aaaaaa");