A new computer based single station VHF system for lightning warning based on broadband interferometer technology is developed. The vertical antenna array was set to get the phase difference of lightning radiation signals, and then the elevation of the arrival signal was obtained. Both the distances of the cloud to ground and cloud flashes can be estimated from the elevations. According to the lightning distance and lighting activity, the different levels of lightning alarm can be given. The error analysis of lightning distance finding indicates that the overall uncertainty of the new method is less than 25% in the range of 50 km, less than 30% in the range of 100 km. The system has been used to detect the lightning during a thunderstorm in Chongqing on 26 July 2011 Thousands of lightning have been detected in the thunderstorm by this system, whose frequency distribution corresponded with the multi station lightning location frequency well. The distance finding results were matched with the multi station lightning location results by using time stamp. The comparison shows that the distance finding errors of most lightning are less than 20%, which proved that the new system can detect lightning in the range of 100 km and play the role of lightning early warning.