The vacuum discharge along the dielectric surface, also called surface flashover, brings significant damages to the vacuum-solid insulation system. Here we implement shape-flexible, complex surface groove microstructures on the dielectric to mitigate the initiation of vacuum flashover. A particle-in-cell (PIC) simulation is employed to reveal the real-time discharge development considering the blockage of the multipactor propagation in the presence of specific surface microstructures. By analyzing the average surface charge density and flashover threshold voltage, it is found that the effect of suppressing surface flashover remarkably augments when the groove number and depth rise up, while such effect gradually saturates when the groove depth reaches a critical value. Furthermore, experiment efforts are devoted to corroborating theory prediction Obtained experiment results show that surface charge accumulation and anode current are alleviated with increasing groove number, with the trend being qualitatively consistent with numerical simulation.