Unlike WordPress or Blogger, Tumblr does not have an official export feature yet, so moving your Tumblr blog to a different blogging platform or taking a backup of the entire blog is rather difficult.
Enter Tumble-log Backup – it’s an online tool that will backup all your Tumblr posts into a single HTML file. You only need to give your tumblr blog name and Tumble-log Backup tool will do the rest.
Tumblr Backup will save all text, photos, audio and video codes.
Since the backup tool doesn’t require a password, you may use it to save an offline copy of virtually any public tumblr blog. And it also works with tumblr micro-blogs that are self-hosted on custom domains like xzy.com instead of xyz.tumblr.com.
Related: Backup Blogger Blogs with Comments