To clarify the regulatory mechanism of NLA on tomato plant architecture and fruit quality, wild-type (WT), nla mutant (narrow leaf angle), and NLA overexpression lines (OE1, OE2) were used as materials, and the study was carried out through genetic analysis, phenotypic and quality determination, and gene expression analysis. The results showed that the tomato leaf angle is controlled by a single gene with semi-dominant inheritance. The nla mutant forms a compact plant architecture due to reduced cell volume at the leaf angle. During vegetative growth, it exhibited significantly increased plant height and decreased stem diameter and crown width. During reproductive growth, it showed significantly higher height of the first inflorescence node and a significantly higher number of the first flowering node. The nla mutant maintained a higher SPAD value during the whole growth period. Mutation of NLA had no significant effect on soluble solids content, but significantly increased flavonoid and titratable acid contents. Meanwhile, the compact architecture optimizes plant spatial distribution, and higher flavonoid content improves antioxidant capacity. Molecular mechanism analysis combined with GA quantification showed that the nla mutant exhibited significantly higher contents of bioactive GA₁ and GA₄, which were closely associated with up-regulated expression of GA biosynthetic genes SlGA20ox1 and SlGA20ox2, as well as down-regulated expression of GA catabolic genes SlGA2ox4 and SlGID1.This study provides a theoretical basis for high-photosynthetic-efficiency breeding and high-quality cultivation of tomato.