At last i found the solution.. We can give sequence number. Settings-> Technical -> Sequence and identifier. -> Create a new sequence for lead.

Then i make editing in the crm_lead.py file. function create edited like this. def create(self, cr, uid, vals, context=None): if vals.get('x_name_lead','/')=='/': vals['x_name_lead'] = self.pool.get('ir.sequence').get(cr, uid, 'crm.lead') or '/' return super(crm_lead, self).create(cr, uid, vals, context=context)

    # context: no_log, because subtype already handle this
    create_context = dict(context, mail_create_nolog=True)
    return super(crm_lead, self).create(cr, uid, vals, context=create_context)