As we all know, tooth growth is very important for children. Whether it is the growth of new teeth or the loss of deciduous teeth, the residual roots of deciduous teeth will affect the physiological replacement of permanent teeth, and the repair of non-absorbable retention posts will also participate. Therefore, the purpose of this article is to explore the polylactic acid can absorb the bending resistance of the root canal pile after repairing the residual root. The method adopted in this paper is to randomly select 24 isolated mandibular premolars to ensure the morphological similarity of the sample as much as possible. After routine root canal treatment and filling, the crown is removed, and the sample is divided into 3 groups on average.. Respectively, polylactic acid absorbable root canal post, fiberglass post and composite resin short post retention, to perform post-core resin crown repair. Subsequently, the electronic universal material testing machine and formula were used to calculate the bending resistance of each material in the fracture mode, and then LSD two-sided inspection was used for comprehensive comparison. Corresponding conclusions are drawn through data comparison. The research results show that the bending strength of the polylactic acid absorbable root canal pile group is 1031.44±359.78N, the bending strength of the glass fiber pile group is 1121.34±193.50N, and the composite resin short pile The group was 1581.36±677.20N, and the differences were statistically significant (P<0.05). The three groups of samples in the experiment are all favorable tooth creases. Therefore, it can be concluded from the experimental results that the bending resistance of the polylactic acid absorbable root canal pile after restoring the residual root is lower than that of the composite resin short pile, which can also meet the clinical needs.