I tried code by guide like this, but it not active: 

class ResPartner(models.Model):
    _inherit = 'res.partner'
    type_customer = fields.Char('Loại KH', default='Normal')
    @api.depends('total_invoiced')
    def _compute_type_customer(self):
        for rec in self:
            if rec.total_invoiced > 1000:
                rec.type_customer = 'Gold'
            else:
                rec.type_customer = 'Normal'