In this talk I will present a new dispersion method to describe two body scattering. Unitarity is imposed well in this method. The amplitudes of different partial waves of pi-pi scattering are obtained. The pole locations and residues are extracted out. Our results show that the poles are more sensitive to the right hand cut rather than the left hand cut，and the latter is constrained well by the former. This new method could be helpful to study general processes of two-body scattering.