Abstract: Since the reform and opening up, with the development of economy, people's quality of life have improved greatly, income level was significantly improved, but income gap is becoming more and more obvious. Cities have the function of promoting economic development, so the disposable income gap of urban residents becomes a key problem that affects the social harmony and stability. The article analyzes differences and trend between 12 western provincial capital cities based on Variation Coefficient,the result shows that Variation Coefficient of disposable income of urban residents in 12 western provincial capital cities expands from 0.115 to 0.204. It indicates that the differences of disposable income of urban residents are gradually increasing. Meanwhile, article analyzes the main reason resulting in differences, eg. central location factors, the level of economic increasing, investment in education and infrastructure.