Changes in the weekend effect index of Lanzhou City during the recent 50 years were calculated using the daily meteorological data, and the changes at different temporal scales were discussed. Whether a similar effect existed or not in holidays was discussed. The results revealed that the intensity of weekend effect in Lanzhou City fluctuated around zero during 1960s-1980s, then raised after 1980s and decreased after 1990s, indicating an obscure weekend effect in recent years. The intensity of weekend effect was higher in winter than in other seasons. The similar effect on holidays has been relatively prominent since 2008. The results demonstrate that, with a higher intensity of human activity, the differences in human activity intensity impacting on the climate between weekdays and weekends slightly decreased, and human activities impacted on climate at the weekend of winters have been strengthened gradually. Human activities on holidays have had a higher impact on the urban climate than that on working days.