According to the 30 climatic stations with climatic records from 1960 to 2009 in Haihe River Basin, the classical calculation methods of agro-meteorological indicators was adopted to analyze the changes of temperature, precipitation and sunshine duration in the past 50 years. With the aid of VIP crop model, the effect of atmospheric CO_2 enrichment, temperature, precipitation and sunshine duration variations on crop yield was study separately. The results show that the north limit of winter wheat moved northward by approximately 70 km in recent 50 years due to the significant temperature rising in winter. Based on the assumption that the irrigation amount and the crop varieties remained same in recent 50years, the wheat yield shows an upward trend (0.2%-3.4%/10 years). Roughly 11%, 0.7%, -0.2% and -6.5% variability of wheat yield can be explained by atmospheric CO_2 enrichment, temperature rise, precipitation decline and sunshine duration decrease, respectively. The positive effect introduced by atmospheric CO_2 enrichment offsets most negative effect introduced by sunshine duration declining, indicating that atmospheric CO_2 enrichment is the main causes of the wheat yield rising. The maize yield shows a downward trend (0.6%~3.8%/ 10 years) in the recent 50 years when the irrigation amount and the maize varieties remained same. Roughly 0.7%, -3.6%, -1.0% and -6.8% variability of maize yield can be explained by atmospheric CO_2 enrichment, temperature rise, precipitation decline and sunshine duration decrease, respectively, indicating that the sunshine duration decrease and the temperature rise are the main causes of the maize yield declining. These results can provide scientific supports for the assessment of the impact of climate change on agriculture and its adaptation countermeasures formulation.