The northwestern Hebei mountains area is located in the transitional area from the subhumid and temperate zone to the semiarid zone, pertaining to the ecologically fragile area. Closing to Beijing and Tianjin, the area is in the windward and upriver area of the two cities. It is of great significance to study the climate change in this area for the purpose of understanding the law of local ecological development and constructing the Beijing-Tianjin ecological protective barrier. Based on the average monthly temperatures and precipitation data collected by three weather stations in the northwestern mountains area between 1956 and 2001, this paper studied the climate changes in this area over the past 46 years, by analyzing the average temperature anomaly and precipitation anomaly of yearly and quarterly, calculating the five years sliding average value of them, and applying the way of univariate linear regression to get linear regression equation of the five years sliding average value. Preliminary research was conducted on the average temperature anomaly and precipitation anomaly values and their development trends with the adoption of correlation analysis. Discussion on factors causing the climate change was carried out. The result shows that the average temperature was on an upward trend in the period 1956-2001 at a rate of 0.41 deg. Celcius /10a, with the highest growth rate seen in winter. In contrast, the annual precipitation was on decrease during the same period at a rate of 7.765mm/10a, with the highest rate seen in summer. The area under research is turning warmer and drier. The correlation analysis indicates no apparent correlation between the upward annual average temperature and the downward precipitation, which should be regarded as a process of independent change. This paper also explores the possible causes that have affected the climate in this area, including the global warming, the climate change in a larger area such as the circulation of water vapor in East Asia as well as the changes to local ecological environment such as pollution, greenhouse gas emissions, increased particulate matters in the atmosphere, ecological damages, etc.