We study the steady optical response of a square lattice in which all trapped atoms are driven by a probe and a coupling fields into the ladder configuration of electromagnetically induced transparency (EIT).It turns out to be a many-body problem in the presence of van der Waals (vdW) interaction among atoms in the upmost Rydberg state,so Monte Carlo (MC) calculation based on density matrix equations have been done after introducing a sufficiently large cut-off radius.It is found that the absorption and dispersion of EIT spectra depends critically on a few key parameters like lattice dimension,unitary vdW shift,probe Rabi frequency,and coupling detuning.Through modulating these parameters,it is viable to change symmetries of the absorption and dispersion spectra and control on demand depth and position of the transparency window.Our MC calculation is expected to be instructive in understanding many-body quantum coherence effects and in manipulating non-equilibrium quantum phenomena by utilizing vdW interactions of Rydberg atoms.