In this study, we used the stem bending resistance index to evaluate the resistance to stem lodging of 200 Brassica napus germplasm resources, based on which, one extreme stem lodging resistance material and one non stem lodging resistance material were screened, and then we measured the content of physical and chemical components in the stems of the two materials at maturity, and carried out the transcriptome sequencing analysis of the stems of the two extreme stem lodging resistance materials at the bud stage and full flowering stage, for laying the foundation for genetic improvement of stem lodging resistance in Brassica napus. The results showed that: (1) the stem breaking resistance and stem diameter of 200 Brassica napus germplasm resources were all normal distribution, which belonged to quantitative genetic traits. The extremely non resistant stem fall material GY172 and anti stem fall material GY199, which had similar birth dates, plant types and stem diameter, but significant differences in stem breaking resistance, were screened based on stem breaking resistance and agronomic traits. (2) The phloem of GY199 was denser than that of GY172, while the content of hemicellulose, lignin, neutral detergent fiber and total soluble sugar in the mature stem of GY172 was significantly higher than that of GY199, while the content of cellulose in the mature stem was extremely significantly lower than that of GY199. The content of cellulose in the mature stem was positively correlated with the stem bending resistance of the two materials. (3) Sequencing of stem transcriptome at bud moss stage and full bloom stage revealed that carbon metabolism, carbon fixation, pentose phosphate pathway, amino acid biosynthesis 14 genes (BnaA10G0056100ZS, BnaC08G0455100ZS, BnaA08G0262400ZS, BnaC08G0239700ZS, BnaA07G0362300ZS, BnaC02G0081300ZS, BnaC04G0273000ZS, etc.) were resistant to stem. The expression was significantly up-regulated in metamaterial GY199, these genes may be involved in regulating stem strength traits and serve as candidate genes for stem lodging resistance in rapeseed.