To investigate the associations of ocular biometric parameters with incident diabetic retinopathy (DR), incident vision-threatening DR (VTDR) and DR progression. This community-based prospective cohort study recruited participants with type 2 diabetes aged 35-80 years from 2017 to 2019 in Guangzhou, China. Refractive error and ocular biometric parameters were measured at baseline, including axial length (AL), axial length-to-corneal radius (AL/CR) ratio, corneal curvature (CC), lens thickness (LT), anterior chamber depth (ACD), lens power and corneal diameter (CD). A total of 1370 participants with a mean age of 64.3±8.1 years were followed up for two consecutive years. During the follow-up period, 342 out of 1195 (28.6%) participants without DR at baseline had incident DR, 15 out of 175 (8.57%) participants with baseline DR had DR progression and 11 of them progressed to VTDR. After multiple adjustments, a longer AL (OR=0.76; 95% CI, 0.66 to 0.86; p<0.001) and a larger AL/CR ratio (OR=0.20; 95% CI, 0.07 to 0.55; p=0.002) were associated with significantly reduced risks of incident DR but were not associated with incident VTDR or DR progression. Refractive status and other ocular biometric parameters investigated, including ACD, CC, CD, lens power and LT were not associated with any of the DR outcomes (all p>0.05). A longer AL and a larger AL/CR ratio are protective against incident DR. These parameters may be incorporated into future DR risk prediction models to individualise the frequency of DR screening and prevention measures.