Abstract: In this paper, principal component analysis was used to probe into urbanization effect on the temperature of Beijing in recent 30 years. Results show that urban heat effect in simultaneity with urbanization is the main cause of urban temperature rise. Estimated proportion of urban heat effect to urban temperature is from 47.5% to 61.2%. Furthermore, correlativity between metropolitan temperature rise and urban population is very strong. Thus this work provides a fundamental reference for the study of urbanization effect on urban climate.