OBJECTIVE To analyze the risk factors of substandard drug blood concentration of meropenem in patients with hospital acquired pneumonia （HAP）. METHODS Totally 130 HAP patients who were admitted to the intensive care unit of Suzhou Hospital Affiliated to Nanjing Medical University from January 2020 to June 2021 and received steady -state blood concentration test of meropenem were selected as the study subjects . The patient ’s age ，sex，body mass and other medical history were recorded . The steady-state blood trough concentration of meropenem was determined and its target was determined . Univariate and multivariate Logistic regression analysis were used to screen the risk factors for the substandard steady -state blood trough concentration of meropenem. The receiver operating characteristic （ROC）curve was drawn to screen the warning value of the risk factors and evaluate the predictive value of the risk factors . RESULTS The steady -state blood trough concentrations of 85 cases were ≥2 mg/L， and those of 45 cases were ＜2 mg/L. Multivariate Logistic regression analysis showed that age ，negative balance and brain injury were independent risk factors for the substandard steady-state blood trough concentration of meropenem （P＜ 0.05）.ROC curve showed that when the patient was 58 years old，the area under the ROC curve was the largest （0.744）， the sensitivity was 0.882，the specificity was 0.556，and the Youden index was 0.438；when the negative balance was 520.5 mL/24 h，the area under the ROC curve reached the maximum （0.827），the sensitivity was 0.722，the specificity was 0.905，and th e Youden index was 0.628. The creatinine clearance rate in the brain injury group was significantly higher than that in the non -brain injury group ，and the steady -state blood trough concentration of meropenem in the brain injury group was significantly lower than that in the non -brain injury group （P＜0.001）. CONCLUSIONS When the HAP patient ’s age is less than 58 years old ，the brain injury and the negative balance is more than 520.5 mL/24 h，the risk of substandard steady -state blood trough concentration of meropenem will increase .