Abstract: Zacang-Chaka salt lake is a typical borate salt lake located in the west part of Xizang autonomous region. PRC. The contents of potassium, boron and lithium there are found higher than those in the other salt lake on Qinghai-Xizang plateau.During evaporation at 25℃, the lake brine crystallizes through steps what "metastable phase diagram"obtained from laboratory indicates. After crystallization of carnallite, high content of boron remained in the concentrated brine. From it boric acid can be separated out by acidification with hydrochloric acid.