Graphene (GR) has excellent physical and chemical properties as a revolutionary material, and its excellent electrical conductivity is critical in developing coagulation electrochemical sensors. Currently, large coagulation testing instruments are complicated to operate and time-consuming, and few point-of-care tests exist for activated partial thromboplastin time (APTT) indicators. To solve this problem, designing and manufacturing a GR-modified electrochemical sensor based on screen-printing technology, which can be used for APTT index detection, is necessary. In this study, the feasibility of chronoamperometry to detect the time principle of activated partial thromboplastin was verified by a thrombin-cleaving thrombin substrate assay. The plasma-activated partial thromboplastin time parameter was measured, and the measurement results were verified using a SYSMEX CS 5100 optical coagulation instrument. The experiments showed that the screen-printed GR-modified electrode had good consistency, and its impedance test coefficient of variation is 2.71%. In the thrombin experiment, the current response intensity of the GR-modified electrochemical sensor was increased by 16 ± 1% as compared to the electrochemical sensor before modification, and the repeated peak time and peak current coefficient of variation are 3.29% and 3.13%, respectively. The APTT values of the three groups of blood samples were selected to show clearly the degree of discrimination, and the peak time variation coefficients of the three groups of APTT repeat experiments are 3.20%, 3.25%, and 2.84%, respectively. The experimental results are linearly fitted with the clinical results of the hospital. R2 is 0.978. The GR-modified enhanced electrochemical sensor showed good repeatability in the APTT test and thus has the potential for immediate detection in a variety of situations.