A double-laser beam lidar to measure potassium (K) layer at Beijing (40.5° N, 116.2° E) was successfully developed in 2010. The parameters of sporadic Ks layers and their distributions were given. The seasonal distribution of Ks occurrence frequency was obtained, with two maxima in July and January. The seasonal distributions of sporadic Es layer occurrence frequency over Beijing differ from those of Ks. However, the good correlation between Es and Ks in the case-by-case studies supports the mechanism of neutralization of metal ions in a descending Es layer.