Objective. To study the clinical efficacy of modified Yiwei Shengyang decoction combined with FOLFOX4 chemotherapy regimen in the treatment of advanced gastric cancer and its effect on tumor marker levels. Methods. A total of 106 patients with advanced gastric cancer who were treated in our hospital from September 2019 to September 2021 were recruited and assigned via random number allocation to receive either FOLFOX4 chemotherapy (control group) or modified Yiwei Shengyang decoction plus FOLFOX4 chemotherapy (observation group). Outcome measures included clinical efficacy and tumor marker levels. Results. Modified Yiwei Shengyang decoction plus FOLFOX4 chemotherapy was associated with a significantly higher efficacy (86.79%, including 22 (41.51%) cases of complete response (CR), 24 (45.28%) cases of partial response (PR), 6 (11.32%) cases of stable disease (SD), and 1 (1.89%) case of progressive disease (PD)) compared to FOLFOX4 chemotherapy alone (47.16%, including 10 (18.87%) cases of CR, 15 (28.30%) cases of PR, 21 (39.62%) cases of SD, and 7 (13.21%) cases of PD) (
P
<
0.05
). There was no significant difference in the levels of CEA and CA19-9 between the two groups before treatment (
P
>
0.05
). Modified Yiwei Shengyang decoction plus FOLFOX4 chemotherapy resulted in significantly lower levels of carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) (2.08 ± 0.47, 15.12 ± 6.74) compared to FOLFOX4 chemotherapy alone (5.46 ± 1.84, 31.82 ± 7.48) (
P
<
0.05
). Conclusion. Modified Yiwei Shengyang decoction plus FOLFOX4 chemotherapy regimen is effective in the treatment of advanced gastric cancer. It regulates the levels of various serum tumor markers in patients and controls the disease, so it is worthy of clinical application and promotion.