Protein phosphatase-1 (PP1) is a member of the Ser/Thr phosphatases and widely distributed in many organisms. The enzyme regulates many important physiological processes, including gene transcription, translation, metabolism, cell growth and division. Three grooves and beta12- beta13 loop in the molecular surface play important roles for binding inhibitors and substrates. Recent research found that beta12-beta13 loop is important for structure and character of the whole enzyme molecule, except for binding inhibitors. Functional research proves that PP1 also regulates transcription process of HIV-1, and relates with causes of many diseases, for example Alzheimer's Disease. This review summarized distribution, molecular structure, enzymatic character, catalytic mechanism and physiological function of the enzyme.