In a large mixing bowl, combine cake mix, mandarin oranges (with juice), eggs, and vegetable oil. Beat with an electric mixer on low speed for 30 seconds, then increase speed to medium and beat for 2 minutes.
Pour batter into a greased 9×13 inch baking pan.
Bake for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool completely.
In a separate mixing bowl, combine crushed pineapple (with juice) and vanilla pudding mix. Mix until well combined.