Gene resources associated with plant stature and flowering time are invaluable for maize breeding. In this study, using an F_2:3 population derived from a natural semi-dwarf mutant grmm and a normal inbred line Si 273, we identified a major pleiotropic QTL on the distal long arm of chromosome 1 (qPH1_dla), and found that qPH1_dla controlled plant height, flowering time, ear and yield traits. qPH1_dla was fine-mapped to a 16 kb interval containing ZmAMP1, which was annotated as a glutamate carboxypeptidase. Allelism tests using two independent allelic mutants confirmed that ZmAMP1 was the causal gene. Real-time quantitative PCR and genomic sequence analysis suggested that a nonsynonymous mutation at the 598th base of ZmAMP1 gene was the causal sequence variant for the dwarfism of grmm. This novel ZmAMP1 allele was named ZmAMP1_grmm. RNA sequencing using two pairs of near isogenic lines (NILs) showed that 84 up-regulated and 68 down-regulated genes in dwarf NILs were enriched in 15 metabolic pathways. Finally, introgression of ZmAMP1_grmm into Zhengdan 958 and Xianyu 335 generated two improved F₁ lines. In field tests, they were semi-dwarf, early-flowering, lodging-resistant, and high-yielding under high-density planting conditions, suggesting that ZmAMP1_grmm is a promising Green Revolution gene for maize hybrid breeding.