It is well-known that the high-voltage withstand ability of vacuum interrupters (VIs) can be increased by conditioning processes. Several conventional conditioning methods, such as spark conditioning and current conditioning, are used by most vacuum interrupter manufacturers. However, the conditioning efficiency of these methods is low and the conditioning energy is high which would lead to an accompanying ‘de-conditioning’ process. The objective of this paper is to propose a conditioning technique for vacuum interrupters by using a series of sub-microsecond voltage impulses that have a high conditioning efficiency and low conditioning energy. Two 7.2kV VIs are used to investigate the improvement of the basic impulse level (BIL) by this proposed technique, compared with the other two VIs which are conditioned by the conventional method. During the conditioning process, VI suffers several hundreds of batches of sub-microsecond high voltage impulses (1000Hz, 0.1s). The peak value of each impulse reaches 100kV. If a breakdown occurs, a high frequency conditioning current of several kA (peak value) would flow through the vacuum interrupter. The experimental results show that this conditioning technology has a higher efficiency compared with the conventional method by decreasing the conditioning process duration from several minutes to tens of seconds. The average value of the BIL voltages by using the new conditioning is 27% higher than that of the conventional conditioning. And the scattering of the breakdown voltage could be reduced by 31%. The conditioned area occupies to the whole contact surface after the high frequency voltage impulses conditioning, which is superior to that of the conventional conditioning.