只需修改以下文件路径： app/design/frontend/default/default/template/(就进到当前网站所有的theme就可以了)

list of files under /templates/:
rss/order/details.phtml

sales/order/items.phtml

sales/order/print.phtml

<?php if ($_order->getDiscountAmount() > 0): ?> 替换为

<?php if (((float)$_order->getDiscountAmount()) != 0): ?>

=====================================================================

sales/order/invoice/items.phtml

sales/order/print/invoice.phtml

email/order/invoice/items.phtml

<?php if ($_invoice->getDiscountAmount() > 0): ?>

替换为

<?php if (((float)$_invoice->getDiscountAmount()) != 0): ?>

=====================================================================

email/order/creditmemo/items.phtml

<?php if ($_creditmemo->getDiscountAmount() > 0): ?>

替换为

<?php if (((float)$_creditmemo->getDiscountAmount()) != 0): ?>

=====================================================================

template/email/order/items.phtml

<?php if ($_order->getDiscountAmount() > 0): ?> 替换为

<?php if (((float)$_order->getDiscountAmount()) != 0): ?>

<td align="right" style="padding:3px 9px"><?php echo $_order->formatPrice(0.00 - $_order->getDiscountAmount()) ?></td>

替换为

<td align="right" style="padding:3px 9px"><?php echo $this->__('-'); ?><?php echo $_order->formatPrice(0.00 - $_order->getDiscountAmount()) ?></td>

(<?php echo $this->__('-'); ?>（到时金额前面会有“-”号显示）)