C-reactive protein (CRP)/albumin ratio (CAR) is a new inflammation-based index for predicting the prognosis of various diseases. The CAR determined on admission may help to predict the prognostic value of multiple trauma patients. A total of 264 adult patients with severe multiple trauma were included for the present retrospective study, together with the collection of relevant clinical and laboratory data. CAR, CRP, albumin, shock index and ISS were incorporated into the prognostic model, and the receiver operating characteristic (ROC) curve was drawn. Then, the shock index for patients with different levels of CAR was analyzed. Finally, univariate and multivariate logistic regression analyses were performed to identify the independent risk factors for the 28-day mortality of multiple trauma patients. A total of 36 patients had poor survival outcomes, and the mortality rate reached 13.6%. Furthermore, after analyzing the shock index for patients with different levels of CAR, it was revealed that the shock index was significantly higher when CAR was ≥4, when compared to CAR <2 and 2≤ CAR <4, in multiple trauma patients. The multivariate logistic analysis helped to identify the independent association between the variables CAR (P=0.029) and shock index (P=0.019), and the 28-day mortality of multiple trauma patients. CAR is higher in patients with severe multiple trauma. Furthermore, CAR serves as a risk factor for independently predicting the 28-day mortality of multiple trauma patients. The shock index was significantly higher when CAR was ≥4 in multiple trauma patients.