This study aims to assess morphological variation of the ring-necked or common pheasant Phasianus colchicus across mainland China in response to environmental factors. We collected 399 pheasant and divided them into two groups: high altitude (>1500m) and low altitude (<1500m). The results that all morphological size measures of males were significantly higher than those of females (P<0.05). Most measures of size at low altitude significantly greater than those at high altitudes, including body weight, body length, and wing length for males (P<0.05), and body weight and wing length for females. The results showed that males and females are different in response to environmental factors. The body weight, wing length, tarsus, skull length and interorbital distance in females were significantly correlated with atmospheric pressure (P<0.05), along with body weight, body length, rictus, wing length, tarsus and skull length in males (P<0.05). A significant positive correlation was observed between wing length of males and wind speed (P=0.017). Conversely, body weight, body length, wing length and tail length in males were significantly negatively correlated with air temperature (P<0.05). Many measures of body size (wing length and tail length for males; tail length for females) increased with latitude after controlling for altitude, indicating that the body size of this species, especially in males, is significantly larger at high latitudes. It is the common pheasant’s adaptability to considerable environmental change that has facilitated the vast distribution of this species.