Objective To investigate the correlation between nutrition related blood biochemical indexes levels and Patient-Generated Subjective Global Assessment (PG-SGA) in preoperative nutritional assessment of patients with gastric cancer. Methods One hundred and seventeen gastric cancer patients who underwent surgery were enrolled in this study by the Department of Gastrointestinal Surgery of West China Hospital. Nutritional status of each patient was evaluated by PG-SGA, in the meantime, nutrition related blood biochemical indexes levels such as transferrin (TRF), prealbumin (PA), albumin (Alb), and hemoglobin (HGB) were measured by analysis of fasting venous blood, then take correlation analysis on the result. Results Eighty cases (68.4%) were in malnutrition (PG-SGA score≥4). The TRF, PA, Alb, and HGB in malnutrition patients were lower than those in non-malnutrition patients (PG-SGA score<4, n=37, P<0.05). The TRF, PA, Alb, and HGB levels of gastric cancer patients had significant negtive correlation with PG-SGA score, the correlation coefficients was –0.629, –0.545, –0.418, and –0.235, respectively (P<0.05). When the PG-SGA score was greater than or equal to 4 points, the optimum cutoff value for TRF, PA, Alb, and HGB was 2.31 g/L, 190.50 mg/L, 38.65 g/L, and 100.50 g/L, respectively (P<0.05). Conclusions The incidence of malnutrition is high in gastric cancer patients preoperatively. The TRF, PA, Alb, and HGB are significantly decreased in the patients with malnutrition, and these indicators has significant negtive correlation with PG-SGA score. The current study indicated that a gastric cancer patient might be in malnutrition when the biochemical levels are less than or equal to TRF 2.31 g/L, PA 190.50 mg/L, Alb 38.65 g/L, HGB 100.50 g/L, and sufficient attention should be paid when any of these occasions appear clinically. The combination of PG-SGA score and nutrition related blood biochemical indexes levels could provide a more accurate assessment of preoperative nutritional status, and the evidence of nutritional intervention for patients with gastric cancer.