With the increasing of tree age, there are problems in the seed trees of Robinia pseudoacaia seed orchard, such as high fruit position, difficult seed collection, low seed production rate and weak tree body. In view of these problems, the trunk of seed trees were truncated and dwarfed to explore the effect of trunk truncating measures and the changing law of nutrient elements. Taking the seed trees in two experimental bases of R. pseudoacacia seed orchard as the research object, three truncating height treatments (0.8, 1.0 and 1.2 m) were conducted respectively in 2016 and 2017, and phenotypic investigation and nutrient content analysis were conducted in 2018. The results showed that the branch length and inflorescence amount of the seed trees with three cutting height in Linghai base were significantly better than those of the non-truncating trees. In the comparative experiment, it was found that the branch length and inflorescence number of the seed trees were the best when the truncating height was 1.0 m; the determination of 10 nutrient elements showed that different truncating height had significant promoting effect on the absorption of both P and Mg element. The results of the research on R. pseudoacacia seed orchard in Jixian base showed that truncating trunk seed trees in 2017 and 2016 were superior to that of non-truncating seed trees, and the cutting measures could significantly improve the length and base diameter of the current-year-branches, and the amount and weight of compound leaves; the trunk truncating trees were conducive to Mg element absorption in 2017. These results could provide a basis for dwarf cultivation and nutrient balance of tree body in the seed orchard of R. pseudoacacia in the future.