A forest fire occurred in Qinyuan County, Shanxi Province on June 5, 2020. Based on the analysis of weather situation, radar echo, lightning location and other multi-source meteorological data, and European Centre for Medium-Range Weather Forecasts （ECMWF） fifth-generation global atmospheric reanalysis （ERA5）,the evolution characteristics of meteorological elements including temperature and precipitation were analyzed in the early stage and during the forest fire, and combined with the field investigation, the cause of the forest fire were given. The results show that the forest fire was caused by a positive lightning, the lightning point was at the edge of convective cloud and the lightning occurred at 15：39 BST on June 5, with the current intensity of 42.2 kA.There was no precipitation in the areas around fire site for 2 consecutive days in the early stage, the 2 m temperature in the areas around fire site increased significantly on the day of the forest fire, with the air temperature of 30-33 ℃, and the precipitation was less than 0.1 mm and it was breezy.

 Based on cloud to ground (CG) lightning data from ADTD and VLF-3D lightning positioning system and lightning disaster records in Shanxi Province in 2017, the temporal and spatial distribution and current intensity of CG lightning detected by  two systems were comparatively analyzed. The results show that the detection efficiency of three-dimensional system to CG lightning was higher than that of ADTD system, and the number of detected lightning by three-dimensional system was twice as large as that of ADTD system. The positioning accuracy of three-dimensional system to lightning disasters was higher than that of ADTD system. The daily (except for the positive lightning) and monthly variation characteristics of monitored CG lightning by three-dimensional system and occurrence time of peak values were basically consistent with ADTD system. Compared with ADTD system, the high-value region of lightning density with 3.0 fl·km-2·a-1 and above from three-dimensional positioning system increased significantly, while the minimum values below 0.3 fl·km-2·a-1 reduced greatly.