By using advanced laser LNM raindrop spectrum detector,precipitation in the mountain area around Miyun Reservoir of Beijing City,was continuously detected from August 2006 to January 2007.Combined with previous methods and research results on raindrop and started from the mechanism that rainfall generates energy,the changes of raindrop characteristics and rainfall energy outside and inside forest canopy in the area were analyzed.The result indicates that average diameter and the median diameter of natural raindrops outside forest canopy decrease with increased rainfall intensity.Raindrop size distribution outside forest canopy is commonly lower than that inside forest canopy.Curve for the relationship between raindrop diameter and cumulative precipitation outside forest canopy is smoother than that inside forest.At low rainfall intensity(≤0.35 mm/h),rainfall energy inside forest canopy is significantly greater than that outside forest canopy.So,it may be agreed that forest canopy can increase the effect of rainfall energy at low rainfall intensity.