  We investigate tunneling behavior between two bright solitons in a
Bose-Einstein condensate with attractive contact interactions between atoms.
The explicit tunneling properties including tunneling particles and oscillation
period are described analytically, which indicates that the periodic tunneling
form is a nonlinear Josephson type oscillation. The results suggest that the
breathing behavior of solitons comes from the tunneling mechanism in an
effective double-well potential, which is quite different from the modulational
instability mechanism for Akhmediev breather and K-M breather. Furthermore, we
obtain a phase diagram for two soliton interaction which admits tunneling
property, particle-like property, interference property, and a resonant
interaction case. The explicit conditions for them are clarified based on the
defined critical distance $d_c$ and spatial interference period $D$.
