Phase transition to chaos of Bose-Einstein condensates in double-well trap with external periodic modulation is investigated in this paper. Particularly, chaos tunneling is studied. It is found that, when resonance between external periodic frequency and natural frequency is established, this system can turn to instability (chaos). The evolutions of Husimi function in quantum condition are discussed. It is found that, when chaos emerges, chaos region and chaos tunneling varies with the interaction between the particles.