The separation and purification of the K and Ca elements in the mineral and the rocks, dating and tracing marine igneous rocks, continental and lunar granites, carbonates, chemical and clastic sediments by using K-Ca system, were described and discussed in this paper. In comparison with the Rb-Sr, Sm-Nd and U-Th-Pb system, the K-Ca isotopic one has its own geochemical behaviors because K and Ca elements belong to the major ones. As mentioned in the text, the different characteristics between the major and trace element systems were shown in the geological process of petrogenesis, matter origin, plate collision, crust-mantle interaction and subduction/turn back,etc. The K-Ca system has already supplied a series of new information and inspiration. With the technological development, the K-Ca system has becomes a new approach to study chemical geodynamics.