Hello Friend, There are two ways to display quantity box on product list page.  

First way to put quantity box on list page:

Find below code on app/design/frontend/YourTheme/YourPackage/template/catalog/product/list.phtml file

<button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="button btn-cart" onclick="setLocation('<?php echo $this->getAddToCartUrl($_product) ?>')"><span><span><?php echo $this->__('Add to Cart') ?></span></span></button>

Put below code instead of above code:

<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" id="product_addtocart_form_<?php echo $_product->getId()?>"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
    <?php if(!$_product->isGrouped()): ?>
        <label for="qty"><?php echo $this->__('Qty') ?>:</label>
        <input type="text" name="qty" id="qty" maxlength="12" value="<?php echo ($this->getMinimalQty($_product)?$this->getMinimalQty($_product):1) ?>" class="input-text qty"/>
    <?php endif; ?>
    <button type="button" onclick="this.form.submit()"><span><span><span><?php echo $this->__('Add to Cart') ?></span></span></span></button>
</form>

 

Second way to put quantity box on list page:

Find below code on app/design/frontend/YourTheme/YourPackage/template/catalog/product/list.phtml file

<button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="button btn-cart" onclick="setLocation('<?php echo $this->getAddToCartUrl($_product) ?>')"><span><span><?php echo $this->__('Add to Cart') ?></span></span></button>

Put below code instead of above code:

<?php $product_id=$_product->getId() ?>
<?php $base_url=Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK);?>
<label for="qty"><?php echo $this->__('Qty:') ?></label>
<input type="text" name="qty" id="<?php echo $product_id ?>" maxlength="12" value="1" title="<?php echo $this->__('Qty') ?>" class="input-text qty"></input>
<button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="button btn-cart" onClick="addToCart('<?php echo $product_id ?>','<?php echo $base_url?>')"><span><span><?php echo $this->__('Add to Cart') ?></span></span></button>

and also put below js at the end of file.

<script type="text/javascript">
function addToCart(pid,purl)
{
	var qty=document.getElementById(pid).value;
	var action=purl+"checkout/cart/add/product/"+pid+"/qty/"+qty;
	window.location=action;
}
</script>

  Thanks,