Abstract： Objective To explore the diagnostic value of color doppler flow imaging (CDFI) on subclinical varicocele(SVC) and the weakening effect of SVC on male fertility.Methods Thirty patients with SVC were exam-ined by CDFI, the diameter and regurgitation duration of spermatic vein were recorded.All semen specimens were rou-tinely analyzed according to the WHO criteria for sperm morphology.Thirty healthy sperm donors were served as con-trols.Results CDFI displayed a widened diameter( 1.94±0.28 mm vs 1.36 ±0.15 mm, P < 0.05 ) and prolonged regurgitation duration[(1.33 ±0.22)s vs(0.43 ±0.16)]s,P<0.05)of spermatic vein in patients with SVC.Sperm density[(20.2±0.1)106/ml vs(86.3±0.6)]106/ml,motihty[(50.7±0.9)% vs(78.5±3.6)]% and vitality [(41.5 ±0.3)% vs (58.7 ±0.6)]% were significantly decreased in patients with SVC compared with those in con-trols (all P< 0.05) ,while the rate of teratospermia remarkably increased in SVC group[(10.5±0.2)vs(4.8±1.7 )]%(P< 0.05 ).Conclusion CDFI was clinically valuable for diagnosis of SVC for its revealing morphological and hemodynamic changes of varicocele.When combined with semen quality analysis,which evaluates the weakening effect of SVC on male fertility, CDFI was suitable to provide the appropriate clinical approaches for SVC therapy.