In order to solve the existing problem of bio-oil, which contains complex compounds and has a high oxygen content, research was conducted on biomass catalytic pyrolysis and reaction mechanisms to enhance the quality of bio-oil and improve the selectivity of monocyclic aromatics hydrocarbon (MAHs). Ga-modified ZSM-5 and Zn-modified ZSM-5 catalysts, prepared through the ion exchange method, were used to investigate the influence of SiO_2/Al_2O_3 ratio and metal element type on the selection of MAHs during corn stalk catalytic pyrolysis. Four different SiO_2/Al_2O_3 ratios (30, 40, 50, and 60) were used for catalyst preparation. Pyrolysis-gas chromatography/mass spectrometry (Py -GC/MS) was used to analyze the products. The results indicated that Ga/ZSM-5 with a Si/Al ratio of 30 achieved the highest relative content of MAHs (19.02%), which was 1.38 times higher than that of the parent ZSM-5 (30). Conversely, Zn/ZSM-5 with a Si/Al ratio of 40 exhibited the highest relative content of MAHs (22.18%), surpassing that of the parent ZSM-5 (40) by 1.51 times. The SiO_2/Al_2O_3 ratio significantly influenced the yield of xylene, naphthalene, and dimethylnaphthalene, while the metal element type also affected the yield of benzene, toluene, and indene. Based on the elemental structure of bio-oil, the relative content of aromatics, and the yield of MAHs, Zn/ZSM-5 (40) performed better than Ga/ZSM-5 (30).