[en] A novel monolayer graphene structure whose unit cell possesses two rectangular defects is proposed. A very obvious dual plasmon-induced transparency (PIT) effect can be successfully achieved by the destructive interference in the terahertz region. The dual PIT effect can be easily tuned by changing the Fermi energy of the monolayer graphene. Since the graphene of our structure exists in a continuous form, we can simply apply a bias voltage to achieve the tuning performance compared to those structures with discontinuous graphene patterns. We have deduced the expression of the theoretical transmittance and the numerical simulation results are very consistent with the theoretical data. Moreover, we find that this structure has a good slow light property and its group refractive index is as high as 545. Thus, the proposed structure and findings may provide a good guidance for the highly tunable optoelectronic devices and excellent slow light device. (paper)