In this paper，the performance of WRF model is validated by simulating wind velocity in January and April over northwestern China，and the errors between simulated and observed values were investigated ． Results show that WRF performance was better in April，when wind speed was big and steady，surface heating strong and temperature increasing faster，but in January wind speed was lower but gust frequently occurred． The relative error in 48 hours at different levels was under 10%，the correlation coefficient ( above0． 8) between observed and simulated values was significant at 90% in April． In January，the mean value of relative error in 48 hours
at different levels was in the range of 20%，and the absolute value of the correlation coefficient was more than 0． 30 and significant at the 99% confidence level． During the two simulation durations，the simulated value was obviously smaller than observed value when wind speed was high． Due to wind dominated by higher level momentum transfer downwards，terrain and thermodynamic function of land surface，the PBL parameters scheme in model is crucial in simulation of wind，especially in northwest China，where vegetable is sparse and terrain complex．

 In recent 50 years, being similar to many water scarcity areas in arid and semi arid regions of the world，the degradation of hydrological cycle and its ecological function and in turn the exacerbation of ecological environment have been occurring over inland river basins in Northwest China.  based on the observed climat。一hydrological data, with the view of interaction among climate, human activities and hydrological cycle, the above mentioned phenomena have been discussed in this paper. 'hhc fact discerned is that hydrological cycle is generating and accompanying as well as coexistence with ecological systems by its various ecological functions.  "hhe overexploitation and utilization of water resources have been beyond the recreating capacity of hydrological cycle and land plain，the dry and in turn the water resources recycle period has been decelerated.  ()wing to the huge arid index in the in warm climate has amplified the negative effect of human activities on hydrological cycle and thus aggra vatcd the ecological
environment.  "hhc human living and economic development arc situated in the area far from the area of mountain water sources in the inland river system，therefore, the approach of integrated water resources management of water shed seems to be an important tool to sustain healthy hydrological cycle or ecosystem as well.