Aim To evaluate the correlation of platelet/lymphocyte ratio (PLR) and risk stratification and in-hospital prognosis in patients with non-ST-segment elevation acute coronary syndrome (NSTE-ACS), and to examine whether PLR combined with Grace risk score can improve the predictive value of Grace risk score for in-hospital major adverse cardiovascular events (MACE). Methods 372 patients diagnosed as NSTE-ACS in the Department of Cardiology, Affiliated Hospital of Qingdao University were selected. According to the PLR level at admission, the patients were divided into low PLR group (PLR<97.56), medium PLR group (97.56≤PLR≤133.32), high PLR group (PLR>133.32), 124 cases in each group. Baseline clinical data, Grace score, and MACE between the three groups were compared. According to the presence or absence of MACE, there were 36 patients with MACE and 336 patients without MACE. The differences in baseline clinical data, PLR and Grace score between the two groups were compared. The correlation between PLR, Grace score and in-hospital MACE was evaluated. ROC curve and DELONG method were used to evaluate the predictive value of PLR combined with Grace score and Grace score alone for in-hospital MACE. Results (1) Grace score, the occurrence of in-hospital MACE and acute heart failure were significantly higher in the high PLR group than the low PLR and middle PLR groups, and the differences were statistically significant(P＜0.001). (2) The age, uric acid, platelet count, PLR, Gensini score, and Grace score were significantly higher in the MACE group than those in the no-MACE group, and the diastolic blood pressure, creatinine clearance rate and left ventricle ejection fraction were significantly lower (P＜0.01). (3) PLR was an independent predictor of in-hospital MACE in patients with NSTE-ACS by multivariate logistic regression analysis. (4) The area under the curve of PLR combined with Grace score to predict the incidence of in-hospital MACE was 0.828, and the area was estimated to be 0.793 by using Grace score alone. The difference between the two areas was statistically significant using the ELONG method of MEDCALC(P＜0.05). Conclusions In NSTE-ACS patients, PLR is an independent predictor of in-hospital MACE. PLR combined with Grace score can significantly improve the predictive value of Grace score for in-hospital MACE.