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Hydrogen peroxide (H₂O₂) is relatively stable among ROS (reactive oxygen species) and could act as a signal in plant cells. In the present work, detached tomato leaves were treated with exogenous H₂O₂ at 10 mmol/L for 8 h to study the mechanism of how H₂O₂ regulates leaf senescence. The data indicated that H₂O₂ treatment significantly accelerated the degradation of chlorophyll and led to the upregulation of the expression of leaf senescence-related genes (<i>NYC1</i>, <i>PAO</i>, <i>PPH</i>, <i>SGR1</i>, <i>SAG12</i> and <i>SAG15</i>) during leaf senescence. H₂O₂ treatment also induced the accumulation of H₂O₂ and malondialdehyde (MDA), decreased POD and SOD enzyme activities and inhibited H₂S production by reducing the expression of <i>LCD1/2</i> and <i>DCD1/2.</i> A correlation analysis indicated that H₂O₂ was significantly and negatively correlated with chlorophyll, the expression of leaf senescence−related genes, and <i>LCD1/2</i> and <i>DCD1/2</i>. The principal component analysis (PCA) results show that H₂S showed the highest load value followed by O₂^•−, H₂O₂, <i>DCD1</i>, <i>SAG15</i>, etc. Therefore, these findings provide a basis for studying the role of H₂O₂ in regulating detached tomato leaf senescence and demonstrated that H₂O₂ plays a positive role in the senescence of detached leaves by repressing antioxidant enzymes and H₂S production.