Incorporated with twisted boundary condition, Polyakov loop correlators can give a definition of renormalized coupling. We employ this scheme for step scaling function in the search of conformal fixed point. Staggered fermion and plaquette gauge action are used in the lattice simulation with six different lattice sizes L = 20, 16, 12, 10, 8 and 6. For the largest lattice size L = 20, we used a large number of GPU’s and accumulated 3,000,000 trajectories in total. We found that the step scaling function sigma(u) is consistent with u in the low beta region. It strongly suggests the existence of conformal fixed point. Some details of our analysis and simulations will also be presented.