Numerical optimization research was made for the dielectric barrier discharge (DBD) reactor for NOx removal in order to improve the efficiency of the DBD reactor. In this paper, the optimization method proposed by our studying team was adopted to carry out the numerical optimization research on the discharge gap of the reactor. As a result, the breakdown strength of reactor was 44.8kV/cm at a 2mm discharge gap and the discharge started at 25μs. When the discharge gap increased to 8mm, the breakdown strength was 34.1kV/cm and the discharge time was 33μs. The removal rates under the two conditions varied little due to the similar electron mean energy, then experiment was conducted to validate the accuracy of the simulation. When the discharge gap increased, the gas handing capacity of the reactor got higher.Therefore, proper discharge gap has important influence on removal efficiency of NO during DBD.