You will find several method on the internet to create height of posts equal. The among the best i believe is "Equal Height Columns with Cross-Browser CSS".

There is however an issue to use that method on joomla module structure and that i could not figure results fine.

I made use of rounded module chrome (with one primary background for module and the other background image for inner DIV to wrap modules bottom) on jooomla template source so each module renders by doing this:

<div class="module_menu">
  <div>
    <div>
      <div>
        <h3>Main Menu</h3>
        <ul class="menu">
          <li><!-- various menu items --></li>
        </ul>
      </div>
    </div>
  </div>
</div>

and that i use 3 module consecutively that covered with a parent or gaurdian DIV. this is actually the code:

<div style="width:904px; margin:20px; float:left; overflow:hidden; position:relative;">
    <div style="width:904px; float:left; position:relative;">
        <div style="width:904px; float:left; position:relative;">
            <div style="float:left; width:288px; height:100%; margin-right:20px;">
                <jdoc:include type="modules" name="user4" style="rounded" />
            </div>
            <div style="float:left; width:288px; height:100%; margin-right:20px;">
                <jdoc:include type="modules" name="user5" style="rounded" />
            </div>
            <div style="float:right; width:288px; height:100%;">
                <jdoc:include type="modules" name="user6" style="rounded" />
            </div>
        </div>
    </div>
</div>

and lastly there's related Css to Joomla modules style:

div.module-gallery, div.module, div.module_menu {
    width:291px;
    background:url(../images/module-bg.png) no-repeat 50% bottom;
}
div.module div div div, div.module_menu div div div {
    padding-right:15px;
    padding-left:15px;
    background:url(../images/module-bg-bottom.png) no-repeat 50% 100%;
    padding-bottom:15px;
    min-height:230px;
}
div.module div div div div, div.module_menu div div div div {
    background:none;
}

How could I set modules height equal automate/dynamically with saving Module background style.

Thanks

You have to have a look in templates/system/html/modules.php.

After that you can produce a copy of module chrome to output your module structure, which may become more advantageous because you code is kinda crazy to see and is not very semantic. i.e.

function modChrome_myModuleName($module, &$params, &$attribs)
{
    $doc =& JFactory::getDocument();
    $css  = ".moduleOuter { your style }";
    $css .= ".moduleInner{ your style }";

    $doc->addStyleDeclaration($css);

    ?>
    <div class="moduleOuter">
       <div class="moduleInner">
        <?php if ($module->showtitle != 0) : ?>
             <h3><?php echo $module->title; ?></h3>
        <?php endif; ?>
        <?php echo $module->content; ?>
        </div>
     </div>
    <?php
}

You'd then guess call the module having a style, like so:

<jdoc:include type="modules" name="left" style="myModuleName" />

There after, you will have a more semantic method of calling your modules and which makes it simpler to obtain your CSS levels to operate.