The survival of species seedlings is closely related to various biotic and abiotic factors. Exploring the effect of key factors on seedling survival can help us to understand species coexistence mechanisms. This study was focused on the woody species seedlings in a 25 hm2 permanent forest dynamics plot in the deciduous broad-leaved forest in the Qinling Mountains, and the generalized linear mixed models (GLMMs) were used to explore the effect of main biotic and abiotic factors on seedling survival. Our results showed that: (1) At the community level, biotic factors played a major role on seedling survival. Seedling survival was significantly negatively correlated with conspecific seedling density and conspecific adult. It also positively correlated with interspecific seedlings density. The results showed that negative density-dependence (NDD) had significant effects on seedling dynamics. (2) At the age class, in addition to biological factors, abiotic factors such as altitude also affected seedling survival. The effect of abiotic factors decreased with the increase of seedling age. In summary, there were various factors affecting seedling survival, among which biological factors were more significant, the main mechanism promoting seedling coexistence was negative density restriction effect in the Qinling Mountains.