Based on the requirement of high current multi-pulse accelerator, the surface flashover characteristics of cross-linked polystyrene (XLPS) material under burst multi-pulse in vacuum were studied experimentally. Vacuum surface flashover experiments were carried out with XLPS samples placed in flat electrodes under single pulse and three pulses with interval of 500 ns. Special phenomena such as continuous decrease of equivalent impedance of vacuum surface before flashover and continuous maintenance of flashover channel after pulse end were observed, and statistical data of vacuum surface flashover of XLPS materials under corresponding conditions were obtained. On the basis of experiments, the flashover characteristics of XLPS in vacuum under high repetition rate multi-pulse loading are analyzed, which provides experimental basis for insulation design of high repetition rate multi-pulse accelerator.