Objective To observe the etiological factors and variation of effects of nontraumatic severe vitreous hemorrhage. Methods A total of 1107 patients (1202 eyes) with nontraumatic severe vitreous hemorrhage who underwent vitrectomy from January 2005 to December 2011 were enrolled in this study. The patients were divided into A group (444 eyes of 415 patients were operated between January 2005 and December 2008) and group B (758 eyes of 692 patients between January 2009 and December 2011) according to admission date. The etiological factors and variations were recorded and retrospectively analyzed. Results Of all 444 eyes in group A, 156 eyes were due to retinal vein occlusion (RVO), 117 eyes associated with proliferative diabetic retinopathy (PDR), 61 eyes with retinal hole／retinal detachment (RH／RD), 42 eyes with Eales disease, 20 eyes with exudative agerelated macular degeneration (EAMD). These diagnoses accounting for 89.19% of the total eyes, were found to be the common causes in patients with severe vitreous hemorrhage, with RVO as the most common cause. Similarly in group B, severe vitreous hemorrhage was found in 347 eyes with proliferative diabetic retinopathy (PDR), 135 eyes with retinal hole／retinal detachment (RH／RD), 133 eyes with retinal vein occlusion (RVO), 25 eyes with Eales disease, 22 eyes with exudative age-related macular degeneration (EAMD), accounting for 87.87% of the total eyes. PDR was the most common cause instead of RVO to vitreous hemorrhage in this group. The number of vitreous hemorrhages increased year by year. Conclusions PDR, RH／RD, RVO, Eales disease and EAMD are the common causes of nontraumatic severe vitreous hemorrhage. There is a trend toward an increasing proportion of PDR among the causes of vitreous hemorrhage.