Small population protection has become an important conservation biology issue because small populations can easily become extinct. Investigating the constraints on small populations and setting up rescue measures are very important tasks in small population protection. Population Viability Analysis (PVA) is the analytical estimation of extinction probabilities. It incorporates identifiable threats to population survival into models of the extinction process. Computer simulation modeling (Vortex) is a tool that can be used to explore the viability of populations subjected to many complex, interacting, deterministic, and random processes. In this study, we investigated the population viability of a troop of Sichuan snub-nosed monkeys (Rhinopithecus roxellana), which are located in the Dapingyu region of the Qinling Mountains, central China. In the winter of 2009, this troop of golden monkey naturally separated into two groups, which were named DPY1 and DPY2. From 2011 to 2015, DPY1 was monitored and data on population size, migration, reproductive system, reproductive rate, mortality rate, mate monopolization, carrying capacity, catastrophes, and harvesting were collected. The DPY2 group was allowed to live in their natural environment and only data on the number of individuals were recorded. Based on the information collected, we used the computer program Vortex 10.0 to simulate the population viability of the Sichuan snub-nosed monkeys in the Dapingyu region. The results suggested that, in the absence of individual migration, the two groups, which had naturally separated from a larger local troop, have 95.8% and 93% possibilities, respectively, of becoming extinct over the next 100 years. When individual migration between the two groups is established, the extinction possibilities can be reduced to 2% and 0.4%. These results suggest that individual migration seems to be the primary limiting factor on long-term troop survival in the Dapingyu region. Therefore, increasing the individual exchange frequency between the groups and making the gene mutation rate equal to the gene loss rate should be encouraged if the long-term survival of this troop of golden monkeys is to improve. Furthermore, programs for improving the protection of Sichuan snub-nosed monkeys in the Qinling Mountains should concentrate on protecting and improving corridors connecting a population to its surrounding populations.