In Custom Module inherit the field using replace tag add default code. In the same code additional add your domains. i.e Single field two or more domain (default openerp domain and your custom domain) condition And or OR based on your requirement.

Yeah That is fine.

But by default they have written two domains in python field.i need to customize that field in xml.how can i write??

def _get_journal(self, cr, uid, context=None):
        if context is None:
            context = {}
        type_inv = context.get('type', 'out_invoice')
        user = self.pool.get('res.users').browse(cr, uid, uid, context=context)
        company_id = context.get('company_id', user.company_id.id)
        type2journal = {'out_invoice': 'sale', 'in_invoice': 'purchase', 'out_refund': 'sale_refund', 'in_refund': 'purchase_refund'}
        journal_obj = self.pool.get('account.journal')
        domain = [('company_id', '=', company_id)]
        if isinstance(type_inv, list):
            domain.append(('type', 'in', [type2journal.get(type) for type in type_inv if type2journal.get(type)]))
        else:
            domain.append(('type', '=', type2journal.get(type_inv, 'sale')))
        res = journal_obj.search(cr, uid, domain, limit=1)
        return res and res[0] or False

i need to add one domain in xml...

<field name="journal_id" groups="account.group_account_user"
                                on_change="onchange_journal_id(journal_id, context)"  domain="[('seq_type', '=', seq_type),]"/>.

i added seq type field in both invoice form and journal form.based on this i am checking domain,but its not working????