Prunus armeniaca Lam. is the dominant species in the wild fruit forest in the Tianshan Mountains and has important values of ecology and resource. The altitude of wild fruit forest is closely linked to its distribution and growth. To clarify the changes of flowering phenological period and floral organs of P. armeniaca in different altitudes, the P. armeniaca forest in Tuergenxinghuagou, Xinyuan County, Xinjiang was selected as the research region from March to April 2021. In the mountainous area of 1000-1500 m with concentrated distribution of P. armeniaca, the sample plots were set up at the altitude gradient of I-V grade from low to high. We monitored the environmental conditions, and investigated the flowering phenological period and floral organ development characteristics of P. armeniaca population. The results showed that:(1) the flowering phenological period of P. armeniaca population lasted about 32 d, and the longest difference of each altitude gradient was 2 d. There was no significant difference in flowering phenological period between the grade I and grade Ⅱ, and there were significant differences between other altitude gradients. The last flowering grade V was 9 d later than the earliest flowering grade I, but the flowering phenological period of the P. armeniaca population was 4 d. The altitude was significantly positively correlated with the flowering phenological period, while temperature was significantly negatively correlated with flowering phenological period; (2) The sepalled length and width, ovary height and width of P. armeniaca were the largest at grade II; corolla diameter, petal longitudinal diameter and transverse diameter were the largest in grade I, while the anther length and width were the largest in grade IV; the style length was the largest in grade V. Altitude was significantly negatively correlated with the external organs and pistils of flowers, and positively correlated with the stamens. Light intensity was significantly negatively correlated with the external organs and pistils of flowers; (3) Climatic factors for the flowering period of P. armeniaca, with significant differences between grade IV, grade V and grade I. Altitude gradient and humidity, light intensity showed significantly positive correlation, altitude gradient and temperature showed significantly negative correlation. The flowering phenological period of P. armeniaca population in Xinjiang lasted about 32 d. As altitude rises, light intensity increases, temperature decreases and humidity increases in P. armeniaca woodlands. The flowering phenological period of P. armeniaca was delayed, and the flowering period increases in duration, with each 100m rise delaying flowering by about 1.8 d; the development of stamens gradually increased, and the development of external organs of pistils and flowers gradually decreased, which was the adaptability of P. armeniaca to altitude changes. The results can provide a theoretical basis for the study on the adaptability of P. armeniaca population distribution.