To systematically evaluate coix germplasm across diverse environments and years， a two-year field experiment （2023–2024） was conducted using 70 accessions planted at two contrasting altitude sites： Shimen （320 m， low altitude） and Luyang （750 m， high altitude）. Seven major agronomic traits—plant height， stem diameter， tiller number， filled grains per plant， seed setting rate， thousand-grain weight， and grain yield—were assessed using variation， correlation， principal component， and cluster analyses. The results revealed substantial phenotypic variation among the accessions. The mean coefficient of variation over the two years at the low-altitude site （16.38%） was significantly higher than that at the high-altitude site （12.63%）， suggesting greater phenotypic plasticity under low-altitude conditions. At the high-altitude site， the performance of most traits—including plant height， tiller number， filled grains per plant， seed setting rate， thousand-grain weight， and grain yield—was superior， reflecting enhanced ecological adaptability. Principal component analysis further confirmed that tiller number， seed setting rate， thousand-grain weight， and grain yield are the key traits driving overall performance. Based on membership function comprehensive evaluation， 11 accessions （YL-8， YL-9， YL-11， YY19-06， YY21-09Y， Y21-12， YY21-30， YY03-06， YY18-2， Xiaoheiken and YY17-33） showed high adaptability across both altitudes. Among these， YY17-33 performed most prominently， achieving an average annual grain yield of 307.14 kg/667 m2 and a seed setting rate of 63.74% at Luyang. This study establishes a phenotypic evaluation for multi-environment and multi-year assessment of coix germplasm and provides valuable genetic resources for breeding programs targeting diverse ecological regions.