Emitting π+π− or η are the first two channels in the hadronic tran-sitions of quarkonium states. In searching for the excited quarkonium states about the open-charm (DD¯ ) or open-bottom (BB¯) threshold via hadronic transitions by Belle, BaBar and BESIII, dozens of new structures have been observed. This number is well above the number of the nominal quarkonium states in the energy regions, which indi-cates the particles beyond the well known quark model may have been observed by experiments. The nature of most of these states, such as Y (4260), Y (4360), Z(3900), Z(4430) and Zb(10610/10650), are still undercover, and they are called ‘exotic states’. This talk will review the exotic states observed in the systems of a quarkonium and a pair of π+π−, a charged π±, or an η. The similiar properties of π+π−/π±/η from the transitions of the exotic states are helpful to figure out the nature of the exotic states. The new intensity frontier experiment Belle II will start data taking in 2018 with the e+e− luminosity increases by 50 times, eight years after the shut down of the KEKB accelerator at KEK, Japan. There will be a unique Belle II data sample for exotic states soon.

                                                  Host: Prof. Wei Wang