In order to improve the modulation depth of the single layered graphene electronic controlled terahertz modulator, a terahertz transmission modulator with an arm type metal mesh structure combined with graphene is proposed. The resonant coupling field excited by the arm type metal mesh structure enhances the interaction between graphene and terahertz wave, which greatly improves the modulation depth of the terahertz modulator when the modulation voltage is applied. The influences on the interaction enhancement of graphene and terahertz wave at different metal structure parameters are analyzed by finite element method simulation. The theoretical results indicate that the arm type metal grid structure increases the modulation depth from 7.7% to 28.2%. On the basis of the theoretical results, the device is fabricated with the photolithography process. The 24% modulation depth is obtained in the experimental measurements, and the experimental modulation depth curve is basically in agreement with the theoretical simulation.