Abstract: The growth status and biomass of mixed forest of Armeniaca sibirica and Hippophae rhamnoides Linn.in Loess Hilly Region of Ningxia were investigated.The mechanism of mixed advantage was analyzed, in order to provide reference for the development of mountain plantation.The results showed that tree height of Armeniaca sibirica in the mixed forest was 17.47% higher than the pure forest on average, and the biomass was 127.7% higher than the pure forest.Carbon sequestration of mixed forests was 3.89 times to pure forests.And mixed forest had higher soil water use efficiency.The slope surface runoff of mixed forest was only 25.1% of that of pure forest, the sediment concentration of runoff was only 59.7% of that of pure forest, and the soil erosion amount was only 17.8% of that of pure forest.The ecological function advantage was obvious.Since the root system of Hippophae rhamnoides Linn.could form special root nodules with frankella in the soil, and effectively fix the free nitrogen in the air by root nodules, the increase of nitrogen in the soil obviously come from the nutrients supplemented by the nitrogen fixation in the root nodules of Hippophae rhamnoides Linn..After the mixture of Hippophae rhamnoides Linn.and mountain apricot, the supply of nitrogen in forest soil was greatly increased due to the nitrogen-fixing effect of root nodules of Hippophae rhamnoides Linn..Sufficient nitrogen supply stimulated the growth of the Armeniaca sibirica,so its growth and biomass increased significantly, showing an obvious growth advantage.In ecological construction, this type of mixed forest could be used as carbon sequestration forest for applying.