The purpose of this study was to acquire the effect of organic carbon fertilizer on biomass and root morphology, and to determine the optimum amount of organic carbon fertilizer in the arid area afforestation, therefore a pot experiment was conducted to study the effect of 6 levels organic carbon fertilizer on biomass, fertilizer utilization rate, and root morphology of 4 plants (Syringa oblate, Swida alba, Pinus tabuliformis, and Fraxinus chinensis). The results showed that significant differences existed in 4 plants’ root and total biomass among the different fertilizer application levels in the test dosage range. The 4 plants’ total biomass increased by 22.41%~82.94%, 42.22%~112.96%, 10.60%~55.59%, and 9.46%~42.61% compared with the control groups, and the maximum value were at level T4 (20 g/strain), T3 (15 g/strain), T5 (30 g/strain), T5 (30 g/strain). With the increase of organic carbon fertilizer application, the fertilizer utilization efficiency of 4 plants decreased by 0.903 kg/kg, 1.946 kg/kg, 0.037 kg/kg, 0.145 kg/kg. The influence of fertilizer on root morphological characteristics (root length, surface area, average diameter, tips, crossings) of S. oblate and S. alba all reached a significant level. Average root diameters of Pinus tabuliformis and Fraxinus chinensis were less affected by fertilizer application, but the other four characteristics showed significant differences under different amount of fertilizer application. Compared with the control groups, longest root length of 4 plants increased by 41.29%~112.77%, the maximum root surface area increased by 34.73%~154.26%, the maximum average diameter increased by 3.85%~42.62%, the maximum tips increased by 47.41%~70.15%, the maximum crossings increased by 22.93%~109.10%. The results showed that the shrub was more sensitive to fertilizer than the tree, but the tree performed better than the shrub at high level fertilizer utilization. The fertilizer utilization for tree should be higher, 30 g/strain for instance, and for shrub shouldn’t more than 20 g/strain in the arid area afforestation.