Four years investigation showed that the farm microclimate has a great change under poplar-crop intercropping system. In comparison with the non-tree control, the average air temperature and wind speed in intercropping farm are decreased by 1.0～1.2℃ and by 32.1%～59.8% respectively, but the relative air humidity is increased by 4.1%～12.2%. And the change of farm microclimate leaded by near-mature poplar stand has the similar consequence. The tree shading degree, on the other hand, becomes more and more serious following with poplar growing. In order to maintain crop output, the intercropping duration will not over 6 years when the poplar spacing is about 20m, but it will prolong for 10 years when it is 30m. It is suggested that the poplar spacing between rows should be over 30m and its branches should be pruned regularly to ensure the stability and long-term of the intercropping system.