Plasma prothrombin is called PT and is traditionally often performed by manual methods, which are easy to perform and have fair accuracy. The reference method of instrument calibration is less reproducible and time-consuming. Nowadays, the instrumentation method is commonly used for testing, which can ensure high accuracy of the test by continuously recording the changes of optical, electrical and mechanical movements during the coagulation process. Fully automated instrumentation method has the advantages of rapid, precise, sensitive and easy. Currently, the instrumentation method is divided into optical method, current method, viscosity method and dry chemical method. The optical method refers to the injection of light during the transformation of fibrinogen into fibrin, and when passing through the reaction device, changes in transmitted light or scattered light occur to determine the end point of coagulation, thus determining the prothrombin time. The current method is based on the property that fibrin is electrically conductive, and uses the characteristics of the circuit connection at the moment of fibrin formation to determine the end point of coagulation. Viscosity method is based on the blood coagulation when the plasma viscosity increases, which can cause the movement of small iron beads moving in the magnetic field to weaken or stop, to determine the end point of coagulation. The viscosity method may not be affected by specimen jaundice, hemolysis, celiac disease or hyperlipidemia. The dry chemical method is to distribute the inert paramagnetic iron oxide particles evenly in the reagent, when the blood coagulation or fibrinolytic reaction occurs, the iron particles will oscillate with it, and the experimental results can be obtained by detecting the bright change caused by the oscillation through the instrument.