Abstract: The XRD analysis shows the "water line" in Qinghai nephrite jade is mainly composed of tremolite. The tremolite fibers in the "water line" part is thinner and longer (several mm) than that of tremolites in the nephrite part, and they parallel to each other. The tremolite fibers in the "water line" is in abrupt contact with the nephrite part. The arrange direction of the fibers is upright to the extend direction of the "water line". The "water line" is formed by filling of ore fluid along cracks in nephrite jade. And the "water line" can not be regarded as the identification characteristic of its origin.