Tunneling is a quantum phenomenon which is forbidden by classical mechanics. Quantum tunneling of microscopic particles has been observed. In fact, quantum tunneling is important to the application of scanning tunneling microscope. However, tunneling of macroscopic objects has not been observed and the related issues have not yet understood. In this talk, I will discuss the tunneling of a two-component atomic Bose-Einstein condensates in a double well. I will introduce quantum-correlated tunneling between two condensates. The relationship between entanglement and tunneling will be discussed. In addition, I will also introduce a new method for manipulating the tunneling dynamics such as the directions of atomic spin flows and single-atom tunneling.