The sustained reproduction is an important landmark of successful adaptation of reintroduced species to climate recovery in the original extinction area. The study of synchronous population reproduction before and after reintroduction can provide accurate breeding prediction information and scientific basis for reintroduction managers. In this paper, we collected the birthing data of the reintroduced Père David’s deer population in Beijing in 1987, 1997, 2007, and 2017. The earliest birthing day of each year was used as a baseline to evaluate the delay in birth of reintroduced individuals and to measure the synchronization rate. ANOVA was used to analyze the effects of temperature, precipitation, air humidity, and light on the birthing timing pattern of reintroduced Père David’s deer. The results showed that, (1) After reintroduction, the annual birth rhythm of the population initially oscillated, then gradually reverted, and finally remained in a relatively stable state. After 85 years (from extinction to reintroduction), the first birthing of the new population in Beijing was delayed by 35 ? 42 days compared with that of Woburn Abbey population. Reintroduction of colonization stage: the birth rhythm of the new population was advanced annually. Population propagation stage: the rhythm of birth was delayed annually. Population recovery stage: the rhythm of birth was re-back slightly year by year and finally remained stable. (2) Deer parturition has more intense periodic timing and synchronization. In the first year after reintroduction, it took 18, 14, and 5 days to achieve 0 ? 25%, 25% ? 50%, and 50% ? 75% of the delivery rate, respectively. The relocation stage, it took 41, 19, and 11 days to achieve the rate of synchronization 0 ? 25%, 25% ? 50% to 50% ? 75%, respectively. In the re-expanding population stage, it took 45, 10, and 9 days to achieve the rate of synchronization 0 ? 25%, 25% ? 50% to 50% ? 75%, respectively. In the restoration phase, it took 24, 20, and 11 days to achieve the rate of synchronization 0 ? 25%, 25% ? 50% to 50% ? 75%, respectively.(3) Cumulative light and accumulated temperature had significant effects on the birth initiation of Père David’s deer but had no relationship with the birth synchronization. The delivery began when the accumulated temperature reached (2748.34 ± 157.69) ℃ and the accumulated light reached (3684.77 ± 514.26) h. (4) There was a correlation between the peak period of birth and aboveground biomass per unit area of reintroduced land. Judging by the rhythm of birth data, the new population has adapted to the climate of the reintroduction site. The number of non-synchronous birth individuals increased annually, but the total span of the delivery period did not extend. Since 1997, the population has had a 30% non-synchronous delivery average year. Therefore, analysis based on birth data reveals that after 37 years of reintroduction, the new population has recovered its adaptation to the habitation where it went extinct 120 years ago.