Background <p>Glycine betaine (GB) not only plays an important role as an osmotic regulator in the regulation of abiotic stress in plants, but also serves as a methyl donor that affects the methylation level of the plant, which in turn affects its growth, development and response to adversity. Tomato as a major crop cultivated in facilities, facility soil salinization has become an important factor limiting efficient and high qualities tomato production. In contrast, little has been reported on the effect of GB on m⁶A methylation and its salt tolerance in tomato. In this study, the effects of exogenous GB on chlorophyll synthesis, photosynthesis and m⁶A methyltransferase in tomato under salt stress were investigated using tomato as experimental material.</p> Results <p>The results showed that 5 mM GB pretreatment alleviated the inhibitory effect of salt stress on the growth of tomato plants. GB promotes the synthesis and accumulation of Proto IX, Mg-Proto IX and protochlorophyllide in the chlorophyll synthesis pathway under salt stress by protecting the activities of CHLH (Magnesium-binding enzyme H subunit) and POR (protochlorophyllide oxidoreductase) thereby increasing the chlorophyll content. In addition, GB improves photosynthetic capacity of tomato by increasing stomatal opening and protecting Calvin cycle enzyme activity. And GB altered the expression level of m⁶A methyltransferase, which in turn indirectly affected the salt tolerance of tomato.</p> Conclusions <p>In summary, GB may enhance tomato salt tolerance by promoting chlorophyll synthesis, enhancing photosynthesis, and regulating the expression levels of m⁶A methyltransferase genes. These findings suggest that exogenous GB application could serve as an effective strategy to improve tomato productivity in salinized protected cultivation systems.</p>