Lodging not only reduces the yield, but also is the most important factor affecting mechanized harvesting. Improving the strength of stalk is an important target for lodging-resistant breeding.In this study, a doubled haploid (DH) population (GZ population) was developed via microspore culture from a cross F1 between the G922 and Zhongshuang 11 (ZS11). Quantitative trait loci (QTL) mapping for stalk strength and its related traits were performed. The main results are as follows: 1. The F1 progeny crossed by ZS11 and G922 had significant mid-parent heterosis in three traits, stalk diameter (SD), stalk rind thickness (SRT) and stalk bending strength (SBS). The correlation between the SBS and four traits, SD, SRT, stalk xylem thickness (SXT), rind penetrometer resistance (RPR), as well as between the RPR and SXT, were all positive significantly. 2. A genetic linkage map was constructed with 1984 SNP markers, and the total length was 2592.64 cM. 90 QTLs for stalk strength and its related traits were detected in four environments, in which 17 QTLs were identified in more than two environments, including six QTLs for SD, five QTLs for stalk strength (SS), two QTLs for SRT and four QTLs for SBS. The major QTL of SD, cqSD.C8-1 could be detected repeatedly in all four environments, and explained 14.67% of phenotypic variation. Two QTL clusters were found on chromosome A2 and C6, respectively, cqSD.A2 consisting of four SD QTLs and cqSS.C6 consisting of four SS QTLs. 3. Stem diameter QTL cluster cqSD.A2 and its three linked molecular markers (Bn-A02-p7893901, Bn-A02-p10176749, Bn-A02-p10668400), QTL cqSD.C8-1 and its two linked molecular markers (Bn scaff_25981_1-p90999, Bn scaff_16287_1-p366585) can be used for molecular marker assisted breeding..This study further enriches the genetic mechanism of stem lodging resistance in Brassica napus, laying the foundation for fine mapping of stem diameter traits and molecular marker assisted breeding.