Purpose: We aimed to investigate the change of three-dimensional (3D) choroidal thickness (ChT), choroidal vessel volume (CVV), and choroidal vessel index (CVI) in young myopic adults using swept-source optical coherence tomography angiography (SS-OCTA) and compare the difference of these indicators in different quadrants of the macula and optic disc. Methods: A total of 248 eye samples from 135 participants were used in this cross-sectional study. Each participant underwent detailed history taking and ocular examinations. Based on axial length (AL), patients were divided into the emmetropia (EM) group, mild-myopia (MIM) group, moderate-myopia (MOM) group, and high-myopia (HM) group. 6 mm x 6 mm (1,024 x 1024 B-scans) SS-OCTA scans were performed centered on the fovea and optic disc. 3D ChT, CVV, and CVI were measured based on a built-in deep learning algorithm. Differences in ChT, CVV, and CVI were analyzed in different regions and different myopic groups. Results: Significant reduction in the global CVV were found in the HM group (1.930 +/- 0.865) in comparison with the EM (3.486 +/- 0.992), MIM (3.238 +/- 1.033), and MOM (2.589 +/- 1.083) groups (p < 0.001). The global CVI was also lower in the HM group (0.258 +/- 0.061) than in the EM (0.320 +/- 0.055), MIM (0.320 +/- 0.051), and MOM (0.286 +/- 0.066) groups (p < 0.001). The ChT was thinner in eyes with HM (242.753 +/- 65.641) than in eyes with EM (377.532 +/- 80.593), MIM (348.367 +/- 78.191), or MOM (300.197 +/- 87.175) (p < 0.001). Compartmental analysis revealed that ChT, CVV, and CVI in the nasal quadrant of the macula and temporal and inferior quadrants of the optic disc were much lower than those in other quadrants (p < 0.05). Correlation analyses found that ChT, CVV, and CVI were negatively correlated with AL and spherical equivalence. Conclusion: 3D ChT, CVV, and CVI gradually decreased as the degree of myopia increased. The changes were more dramatic on the nasal side of the macula and the temporal and inferior sides of the optic disc. These findings demonstrated the 3D choroidal change and highlighted the papillo-macular bundle as a sensitive region in myopic development.