Why is there a  tag where I didn't add it? I put the following code into the bock content box and set the input type to Full HTML; then I enabled it on page--front.tpl.php. When I viewed the HTML source, I
saw the &lt;a&gt; label contained a &lt;p&gt; tag.  

  &lt;ul&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
       &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a href="addons.html"&gt;&lt;img class="floatleft" src="images/Panel-index03_108.jpg" /&gt;&lt;p&gt;&lt;strong&gt;test&lt;/strong&gt;&lt;br/&gt;
      Fujia Chanpin 01&lt;/p&gt;&lt;/a&gt;&lt;/li&gt;
    &lt;/ul&gt;


For example, for the last list item, the output was the following.

&lt;a href="addons.html"&gt;&lt;img src="sites/all/themes/cpanel/images/cPanel-index03_108.jpg" class="floatleft"&gt;&lt;p&gt;&lt;strong&gt;tsdet&lt;/strong&gt;&lt;br&gt;Fujia Chanpin 01&lt;/p&gt;&lt;p&gt;&lt;/p&gt;&lt;/a&gt;


Why is there a &lt;p&gt; tag where I didn't add it?
For not getting the paragraph tags, you need to use an input format that does not include the Lines and paragraphs break automatically setting.

Check to see if Convert line breaks into HTML input format is enabled in admin/config/content/formats/full_html, and disable it. You can still add &lt;p&gt; and &lt;br&gt;, but Drupal will not add them automatically for every line break present in the text.