The chemical composition of ancient white porcelain in Beijing Longquanwu kiln in 4 different historical periods of early Liao Dynasty, middle Liao Dynasty, later Liao Dynasty and Jin Dynasty are analyzed by micro-X-ray fluorescence focused by polycapillary optics. The experimental data are carried out by factor analysis. The results show that ancient white porcelain in different historical periods in Beijing Longquanwu kiln can be divided into two sorts according to their chemical compositions. The one center of ancient white porcelain is that of early Liao Dynasty, and the other is that of middle Liao Dynasty. The chemical composition of ancient white porcelain in later Liao Dynasty and Jin Dynasty are similar to that of early Liao and middle Liao, respectively. There is no significant difference of chemical composition of ancient white porcelain between the ancient fine white porcelain and ancient coarse white porcelain. The experimental result does not support the hypothesis that Beijing Longquanwu kiln is GUAN kiln in history. Moreover, the high content of minor element Sr is the characteristic of chemical composition of ancient white porcelain in Beijing Longquanwu kiln.