To investigate the independent risk factors for a decreased hemoglobin level in gastric cancer patients undergoing adjuvant chemotherapy. A retrospective study was conducted on 142 gastric cancer patients who received chemotherapy between May 2017 and May 2021 at the Gansu Provincial Cancer Hospital. All patients were subjected to the same regimen of adjuvant chemotherapy combining platinum/taxane and fluorouracil. The correlation between patients' clinicopathological features and the decreased hemoglobin during adjuvant chemotherapy was analyzed. Logistic and LASSO regression analyses were employed to screen for independent risk factors for decreased hemoglobin during adjuvant chemotherapy. Univariate analysis revealed that intraoperative bleeding, pre-chemotherapy anemia, and hypoalbuminemia were risk factors for the decreased hemoglobin in patients during adjuvant chemotherapy (all P < 0.05). Both logistic and LASSO regression analyses corroborated these factors as influential factors in the decrease of hemoglobin (P < 0.05). In addition, both logistic and LASSO regression models demonstrated similar performance in this aspect. The nomogram model was subjected to internal validation, resulting in a C-index of 0.712 (0.629-0.796). The calibration curves exhibited satisfactory alignment with the ideal curve. Intraoperative blood loss, pre-chemotherapy anemia, and hypoalbuminemia are independent risk factors for hemoglobin reduction following chemotherapy. Moreover, both the logistic and LASSO regression models exhibited equivalent performance in this context. These findings bear substantial clinical implications, aiding physicians in the management of anemia in patients undergoing chemotherapy.