Platelets play a pivotal role in the thromboembolic, inflammatory, and immunomodulatory process. The alteration of platelet quality often affects the treatment and prognosis of critically ill patients, and has a significant correlation with mortality. With the further research on the function of the platelet, it is found that the abnormal platelet quality can present during the early stage of the illness of the critically ill patients. In order to evaluate the alterations of the platelet quality more accurately, the further studies of platelet parameters, including platelet counts (PLT), platelet hematocrit (PCT), platelet large cell ratio (PLCR), mean platelet volume (MPV), platelet distribution width (PDW), immature platelet fraction (IPF) and so on, are still be the focus of current researches in the field of critical illness. At the same time, the application of thromboelastography/thrombelastography-platelet mapping (TEG/TEG MP) to the measurement of platelet function, especially the researches on the inhibitory rate of adenosine diphosphate (ADP) and the inhibitory rate of arachidonic acid (AA), is the hot spot of current researches. With regard to the diagnosis, prognosis and early goal-directed therapy (EGDT) of the critically ill patients, it is important to comprehensively apply the methods of platelet function evaluation.