The main types of clastic sandstones are feldspathic litharenite and lithic arkose in the Cretaceous of the Songliao basin. There are many unstable components containing detrital feldspar, lithic fragments and so on. Content of potash feldspar decreases with increasing burial depth increases (increasing diagenesis) and gradually disappears below a depth of 2700 m in detrital feldspar of sandstone. The albite component increases while anorthic component decreases in detrital plagioclase. The plagioclase turned into an end - member component of albite. In the diagenic process, three types of albitization are determined; (1) albitization of metasomatism by means of cation exchange in detrital feldspar; (2) secondary growth of albite on the original detrital feldspar; (3) albite crystallization with detrital feldspar solution. Analysis based on the equilibrium activity of thermodynamic principle shows that albitization of plagioclase is not controlled by temperature and pressure in diagenesis, and that albitization of potash feldspar depends on the increase of temperature and pressure during a diagenetic process. Therefore, the albitization of plagioclase is shown in the early stage of diagenesis and albitization of potash feldspar appears only in the late stage of diagenesis.