In order to increase wood production, selection of suitable tree spacing and cultivation of different crops between tree rows, especially at early years would increase productivity and poplar cultivation area. In the study Populus alba seedlings were planted in a randomized complete block design with three replicates and fourth mixed poplar and alfalfa treatments with tree spacings including 3×4, 3×6.66, 3×8, and 3×10 m also two control treatments. We investigated some important attributes during 2009-2013. Tree diameter and dry weight were measured. The data were analyzed using combined analysis of variance. Results showed that there were not significant differences between treatments in average of height growth. First and second years revealed most amount of height growth. Of course for diameter growth, first and fourth years revealed best results. Mixed 3×4 treatment showed highest wood volume growth.  Also the most amount of dry weight production of alfalfa belonged to pure alfalfa and 3×10 treatments. All of the attribute amounts revealed differences among treatments were significantly different at 5% level of probability. For the some attributes there were significant differences among years and interaction between treatments and years. As a final result until this stage the suitable planting spacing of tree in Poplar/alfalfa intercropping system in Azarbayjan province is 3×8 m according to the site conditions.