A groove spoiler can effectively reduce vehicle sunroof buffeting noise. In order to have a better understanding of sunroof buffeting noise reduction mechanism associated with groove spoilers, a test platform of groove and uniform spoiler was built. Wind tunnel experiments were performed to investigate the surface pressure field downstream of uniform and grooved spoilers and to observe the effects of the grooves on the wall pressure. The test results show that the presence of grooves in the spoiler moves the reattachment point upstream and reduces the recirculation region length. Compared with the uniform spoiler, an initial spanwise phase difference was observed behind the spoiler in the presence of the groove, which decreased the coherence of the wall pressure, and the wall pressure had a big decay rate in the spanwise direction. Grooves in the spoiler can obviously disturb the downstream flow, and thus it can weaken the primary aerodynamic excitation for the vehicle cabin.