Background: To evaluate the value of transvaginal three-dimensional power Doppler ultrasound (3D-PD-US) in quantitative assessment of early diminished ovarian reserve (DOR) among perimenopausal women. Methods: A total of 166 perimenopausal women with DOR were selected from February 2019 to December 2022, including 63 in the early stage and 103 in the mid-to-late stage. Ovarian reserve was assessed by biochemical testing and 3D-PD-US imaging. Biochemical indicators included antimüllerian hormone (AMH), basal serum follicle stimulating hormone (FSH) and estradiol (E{}_2). 3D-PD-US indicators involved ovarian volume (OV), antral follicle number (AFC), vascularization index (VI), blood flow index (FI), and vascularization flow index (VFI). The accuracies of two methods were compared. Results: There were significant differences in OV, AFC, VI, FI, and VFI between the early DOR group and the mid-to-late DOR group (all p 0.05). FSH had significant negative correlations with OV, AFC, VI, FI and VFI, with correlation coefficients of –0.342, –0.381, –0.179, –0.123, and –0.175, respectively (all p 0.05). Conclusions: 3D-PD-US may serve as a quantitative method for early detection of DOR in perimenopausal women.