Just lets follow the steps below:-
1. Login into your Digg account.
2. Click Settings at the right top of the page.
3. Click Import Feeds at the left task pane.
4. Enter your Website’s RSS Feed URL in the Text box.
5. Select your site’s niche from the dropdown box and click the Add Feed button.
6. After submitting the feed you need to verify your ownership of your Site, by following any one of the two methods provided by Digg.
See Image Below