Observed across a large altitudinal gradient and a widely-distributed geographical range, the tree sparrow (Passer montanus) is a species commonly associated with human beings. This study analyzed the relationship between 10 morphological characteristics of 837 tree sparrows sampled, and 4 environmental factors (air temperature factor, sunshine factor, altitude factor, and air-speed factor). The results indicated that morphological traits, such as body weight, rictus, wing length, tail length, tarsus length, skull width, and interorbital distance were significantly correlated with the sunshine factor (P<0.05). Moreover, body weight, body size, wing length, tail length, and tarsus length were significantly correlated with the altitude factor (P<0.05). Additionally, body weight, culmen length, wing length, and skull length were significantly correlated with the air temperature factor (P<0.05). The aforementioned findings suggest that these morphological characteristics have adaptive potential in response to environmental factors. Furthermore, we analyzed the relationship between morphological size and latitude by controlling for longitude and altitude. The results of this analysis indicated that body weight, wing length, and skull size had a significant positive correlation with the latitude factor (P<0.05). Conversely, culmen length and rictus had a significant negative correlation with latitude (P<0.05) after controlling for longitude and altitude. These findings suggest that body size increases with rising latitude, while bill size decreases with increased latitude. Therefore, we conclude that the morphological variation of this species is in concordance with Bergmann's rule and Allen's rule. A significant positive relationship was found between flight ability and the altitude factor (n=92, r=0.217, P=0.038), and thus our results postulate that the flight ability of P. montanus is greater at higher altitudes than at lower altitudes. This adaptive component of flight ability may offer an explanation as to why P. montanus is so widely-distributed throughout the planet.